Download Notes - Humble ISD

Name _____________________________________________________________________
Test Date ______________
UNIT 8 - INTRODUCTION TO GENETICS
Although the resemblance between generations of organisms had been noted for thousands of years, it wasn’t until the 1800s that
scientific studies were carried out to develop an explanation for this. Today we know that we resemble our parents because of
_______________, which is the set of characteristics we receive from ______________________. The study of heredity is known as
_________________.
I. SEXUAL REPRODUCTION & MEIOSIS
(pp. 270-276)
In sexual reproduction, an egg and sperm cell fuse together to create a fertilized egg or _______________.
A. Chromosome Number
1. Somatic Cells - _____________ cells
 Human somatic cells contain ________ chromosomes
 ______________ or ________ meaning they contain a ____________ set of chromosomes, half ( _____ ) from
_________ and half from ________.
 “Matching” chromosomes are known as __________________________________________. A homologous pair is
made up of a copy of a chromosome from each parent, with the same ___________.
2. Gametes - ___________ and _______________ cells
 Human gametes contain ______ chromosomes.
 ______________ or ______ meaning there is _____ set of instructions for each ______.
 When gametes fuse together in _____________________, the ________________ produced is _____________ and
has _______ chromosomes.
B. Meiosis
 Special type of cell division that only occurs in specialized germ cells in _______________ of females and ______________
of males.
 In meiosis, DNA is replicated once but cell divides ___________, resulting in ______ cells with _______ the original
chromosome number.
 In females, process is known as ________________________.
 In males, process is known as _________________________.
 In both males & females, prior to meiosis I, DNA is replicated during ______ of _____________________________.
Meiosis occurs in two stages:
1. Meiosis I
 Prophase I
 Unlike prophase of mitosis, ___________________________ come together to form a ______________.
 Tetrads are held together at the _____________________.
 Crossing Over
 Exchange of genetic information between a ________________________________ with its
___________________________________.
 Occurs very frequently
 Allows for ________________________________________________________________.



Metaphase I
 _____________________________ align in equator of cell
 Each homologue consists of _______________________________________.
Anaphase I
 __________________________________________ are pulled apart
 __________________________________, _________________________ still intact
Telophase I
 Two cells are formed, each with _______ chromosomes
 Each chromosome still composed of two ___________________
 Two cells produced at the end of meiosis I are _______________ because ________________________
__________________________________
2. Meiosis II
 Continues with the two cells formed moving directly into prophase II without any further _____________________ of DNA.
 In anaphase II, ______________________________________ are pulled apart.
 Two new cells are formed from each of the two cells formed in meiosis I, resulting in a total of ___________ new cells, each
with ____________the original number of chromosomes.
 Cells produced are called ____________________.
3. Oogenesis vs. Spermatogenesis- See drawings of differences between meiosis in males & females
 Males produces 4 viable sperm cells
 Females produces only one egg and 3 polar bodies
II. HISTORY OF GENETICS
(pp. 277-280)
A. Gregor Mendel
 Known as the “Father of _______________”
 Famous for his experiments with ________ plants.
 Used true-breeding pea plants, which means ________________________; characteristics always show. Known as the
____________ generation.
 Studied seven ______________, including plant height, seed color, flower color, etc.
o A trait is an ________________________________.
 Pea plants cross-pollinate, meaning pollen from one plant fertilizes an egg from another, but they can also selfpollinate, meaning pollen can fertilize egg from ______________ plant. Mendel controlled the fertilization process of the
pea plants by preventing __________________________________ and controlling
___________________________________.
B. Mendel’s Results
 P generation – Crossed __________________ plants with one trait with ________________ plants
with the
other. For example, _____________________________________________
 F1 generation – Offspring produced from _________________. In F1, one trait ____________. For example, tall plants
X short plants = __________________________.
 F2 generation – Offspring produced from _________________. In F2, trait that disappeared in F1
reappeared
in __________ of the offspring; the other ¾ showed _____________________________.
C. Mendel’s Principles – After analyzing his results carefully, Mendel formed conclusions that increased
understanding of inheritance and opened the door for the study of genetics.
 Individual units called ___________ determine inheritable characteristics. A gene is a portion of ___________ that
codes for a specific ____________.
 For each gene, an organism inherits two alleles, one from each __________________. Alleles are
different forms or ____________________ of a ___________. For any given trait,
o If an organism is ___________________, its alleles are the same and the trait will be expressed.
o If the alleles differ, the organism is said to be ___________________ for that trait and only one allele
will be expressed. The expressed allele is the ______________ allele, designated by an __________-case letter.
The allele that is not expressed in a heterozygous trait is _________________, designated by a
_____________-case letter. A recessive allele is only expressed when an organism is ________________.
 Principle of Segregation - In meiosis, the two alleles for a trait segregate (_______________). Each egg or sperm cell
receives a copy of one of the two alleles present in the somatic cells of the organism. There is a _________ chance that a
copy of that allele will end up in the gamete produced.

Principle of Independent Assortment – The way one pair of alleles segregates has no influence on any other pair of
allels.
D. Genetics Terminology
 Phenotype - ________________ description of trait; for example, ______________
 Genotype – ______________________ of an organism; for example, ____________________
 If round pea seeds are dominant to wrinkled pea seeds, round is designated ____ and wrinkled is designated ______.
o Homozygous dominant
 Genotype = __________________________
 Phenotype = _________________________
o Heterozygous
 Genotype = __________________________
 Phenotype = _________________________
o Homozygous recessive
 Genotype = __________________________
 Phenotype = _________________________
III. ANALYZING INHERITANCE
(pp.280-282)
A. Probability
Due to the Law of ___________________, if you know the genotype of the parents, you can predict the likelihood of a
trait occurring in the offspring. Probability can be written 3 ways; for example, the probability of a coin coming up
heads after being flipped is (fraction) _____, (ratio) ________, or (percent) _______.
B. Punnett Squares
A Punnett square is a tool used to predict the possible outcomes of _______________ and ____________________;
in other words, a Punnett square is used to determine the probability of certain traits appearing in offspring.
IV. PUNNETT PRACTICE
**Please note: To earn full credit, you must include a key and cross with each problem!**
A. Construct a Punnett square to determine the probability of white flowers if a heterozygous purple (Pp) flower is
crossed with a homozygous white (pp) flower.
Key: _________________________________________
Cross: ________________________________________
Probability of white flowers = ___________________
B. Construct a Punnett square to determine the probability of short pea plants if a homozygous tall (TT) plant is crossed
with a heterozygous tall (Tt) plant.
Key: _________________________________________
Cross: ________________________________________
Probability of short pea plants = _________________
Probability of tall pea plants = ___________________
C. If round peas are dominant over wrinkled peas, make a Punnett square to determine the genotype and phenotype
ratios of the offspring if a heterozygous plant is crossed with a homozygous recessive plant.
Key: _________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
D. Use a Punnett square to determine the genotype and phenotype ratios of the offspring from a cross between a
homozygous dominant yellow pea pea plant and a homozygous recessive green pea pea plant.
Key: _________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
V. DIHYBRID CROSSES
The Punnett squares we have been doing are known as ________________________ crosses, meaning that only
one trait has been considered at a time. In a dihybrid cross, ________ different ____________ on 2 different
_____________________ are analyzed.
A. Peas homozygous for round shape and heterozygous for color are crossed with yellow peas heterozygous for shape
Key: R = round, r = wrinkled; Y = yellow, y = green
Cross: ________________________________________
Genotype ratio: _______________________________________________________________________________
Phenotype ratio: ______________________________________________________________________________
B. Key: G = gray body, g = black body; R = red eyes, r = black eyes
Cross: GGRr X Ggrr

What are the phenotypes of the parent fruit flies? _________________________________
Cross: __________________________________________
Genotype ratio: _____________________________________________________________________________________________
_____________________________________________________________________________________________
Phenotype ratio: ____________________________________________________________________________________________
____________________________________________________________________________________________
VI. A CLOSER LOOK AT HEREDITY
(pp. 302-304)
A. Incomplete Dominance – Neither allele has “complete” dominance over the other - heterozygous phenotype is a
____________________________________________________

For example, in snapdragons, ____________________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
B. Codominance – Both alleles _____________ dominance and are always __________________ if present.

For example, ________________________________________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
C. Polygenic Traits – “_________________________” Many traits are controlled by more than one gene. Examples include
_____________________________________________________
D. Multiple Alleles – Many genes have more than ___________ alleles, although an individual only has ____ alleles for the gene. An
example is _______________. There are _______ possible alleles for this gene.