Download Genetics Study Guide KEY Genetics study guide

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Genetics Study Guide
Study Resources:
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Our Genes, Our Selves
Pages 112-123 in your Sciencesaurus.
All lesson worksheets 54 -71 and answer keys
Science Notebook, vocabulary page and/or glossary
Part A: Fill in the table below with the definition of each vocabulary word in the first column and an
example or drawing in the second.
Word
Chromosome
Gene
Allele
Characteristic
Trait
Asexual
Reproduction
Sexual
Reproduction
Definition
Example/Drawing/Sentence
A string of DNA that contains the genes for Human body cells have 46 chromosomes.
an organism.
X
Information inherited from parents
A version of a gene
A quality of something or something that
can be observed
A version of a characteristic
Reproduction requiring only one parent;
offspring receive genes from one parent.
Reproduction requiring two parents;
offspring receive genes from both parents.
Offspring
A new organism that is created by one or
two parents
Word
Clone
Definition
Example/Drawing
An exact copy of a parent organism
Dominant
A version of a gene that, if present
determines a trait
Recessive
A version of a gene that is hidden if a
dominant version is present
Homozygous
To have two of the same allele
Heterozygous
To have two different alleles
Genotype
The genes an organism has
Phenotype
The physical traits that show up on an
organism (how they appear).
Part B: Big ideas.
1. How is a condition like Marfan Syndrome different than a disease like the flu?
Marfan Syndrome is a genetic condition. It is inherited from parent to offspring. You cannot catch it. It
can be treated but not cured. The flu is an infectious disease. It is contagious, meaning that you can
catch it from anyone who has it, even if you are not related. You can prevent the flu by washing your
hands or getting a flu shot. The flu can be cured with proper rest, nutrition, and a healthy immune
system.
2. Describe three ways that offspring from sexual reproduction are different from offspring from asexual
reproduction:
 Number of parents: Sexual reproduction requires two parents; asexual reproduction requires
only one parent.
 Genes of parents compared to genes of offspring:
Offspring of sexual reproduction get half their genes from each of their parents, so they will
have a unique combination of their parents’ genes. Offspring of asexual reproduction are an
exact copy of their parents, so their genes are the same as their parent’s.
 Genes of siblings compared to each other:
Offspring of sexual reproduction have different gene combinations from each other EXCEPT in
the case of identical twins. Identical twins have identical genotypes. Offspring of asexual
reproduction will all have the same genotype.
3. Why are dominant traits more likely to be seen in offspring of two heterozygous parents (Tt) than a
recessive trait?
There are three possible ways that an offspring will inherit the dominant phenotype. The genotypes TT,
Tt, and tT all result in a dominant phenotype. There is only one allele combination that will result in a
recessive phenotype: tt. This makes the dominant trait more likely at a 3:1 ratio.
4. How is a clone different from an identical twin?
A clone is the offspring of one parent (asexual reproduction) and has the exact same genes as that
parent and their siblings. An identical twin is the offspring of two parents (sexual reproduction) and has
the exact same genes as their identical sibling. However, identical twins will have a different genotype
from their parents.
5. How is an identical twin different from a fraternal twin?
Identical twins result when one sperm fertilizes one egg and then that fertilized egg splits into two
offspring. Fraternal twins result when two sperm fertilize two eggs and two offspring are created.
Fraternal twins have different gene combinations from each other. Identical twins have the same
genes as each other.
6. How can you make scientific studies of genetics more reliable?
Studies of genetics require lots and lots of trials for their results to be reliable. Inheritance in sexual
reproduction occurs randomly and more trials allows patterns of inheritance to become more obvious.
7. How are human body cells different from human sex cells?
Human body cells have 46 chromosomes (23 pairs). Human sex cells (eggs and sperm) have 23
chromosomes and no pairs. A sperm and egg must combine to make a new human body cell with 46
chromosomes.
8. How can the environment impact an organism’s phenotype (how they look)?
An organism may have the genotype for a particular trait, but may require proper nutrition,
experiences, or some other aspect of their environment for the trait to be seen in their phenotype. For
example, a person may have the genotype for being tall, but will require proper nutrition to reach their
maximum height.
9. What are three possible effects of a mutation?
Some mutations are harmful, like Marfan Syndrome. Other mutations are harmless. Some mutations
can be helpful.
Part D: Complete the following questions about Punnett squares.
1. Name the dominant trait and explain your reasoning.
a. Two short tailed mice were crossed. Some of the offspring have long tails.
Short tails are a dominant trait because the offspring have a trait which neither parent
displayed. Dominant traits overpower recessive traits. Recessive traits can reappear if offspring
are homozygous for the recessive allele.
b. A brown horse is crossed with a black horse. All the foals are black.
Black is the dominant trait because none of the offspring display the brown phenotype.
2. Identify the following genotypes as homozygous dominant, homozygous recessive or heterozygous.
Dd heterozygous
DD homozygous dominant
dd homozygous recessive
3. The allele for brown eyes (B) is dominant over the allele for blue eyes (b).
a. What are the genotype and phenotype for a homozygous dominant individual?
BB, brown
b. What are the genotype and phenotype of a homozygous recessive individual?
Bb, blue
c. What are the genotype and phenotype of a heterozygous individual?
Bb, brown
4. Yellow seed color is dominant to green seed color. Complete the following cross: Yy & YY
Y
y
Offspring Genotype Probability:
Y
YY
Y
YY
Yy
2YY: 2Yy
½ or 50% YY; ½ or 50% Yy
Yy
Offspring Phenotype Probability:
All yellow seeds;
5. Green leaf color is dominant to white leaf color. Cross two heterozygous green plants.
L
l
Offspring Genotype Probability:
L
l
LL
Ll
Ll
ll
1 LL:2Ll:1 ll
¼ LL, ½ Ll; ¼ ll
25% LL, 50% Ll; 25% ll
Offspring Phenotype Probability:
3 green: 1 white
¾ green; ¼ white
75% green; 25% white
6. If a parent with type A blood is crossed with a type B parent and half the offspring are A and the other
half are AB, what are the possible genotypes of the parents and the offspring?
Parents: Parent A: AA; Parent B: BO
Offspring: AB offspring: AB; A offspring: AO
Part E: Use the pedigree below to answer the following questions. The shaded parts of the diagram are used
to identify family members who have brown eyes.
1. What is this type of diagram called? Pedigree
2. What do the circles represent? females
3. How many children (generation 2) did Mr. and Mrs. Lopez have? four
4. How many of the Lopez children (generation 2) were males? two
5. Was the oldest Lopez child a girl or boy? girl
6. What color are Mrs. Lopez’s eyes? blue
7. How many children (generation 2) have blue eyes one
8. How many generations of the Lopez family are shown on the diagram? three
9. What color eyes does the granddaughter of Mr. and Mrs. Lopez have? brown
10. What color eyes seems to be dominant and how can you tell? Brown is likely dominant, but all parentoffspring situations are possible whether the shading represents a dominant or a recessive trait. Either
way, we know the parent with a dominant trait must be heterozygous if the spouse is recessive and
they have a recessive offspring.