Download Chapter 11 Intro to Genetics

Chapter 11 Intro to Genetics
11-4 Meiosis
A. Principle of genetics requires 2 things
1. A single copy of every gene must be inherited
2. When gametes (sperm/egg) are formed a
process must separate the 2 sets of each gene
so that each gamete has only 1 set of genes
B. Chromosome number
1. somatic cell (body cell) has 46 chromosomes
a. 23 from female gamete (egg)
b. 23 from male gamete (sperm)
c. Homologous chromosomes
--corresponding chromosomes of male and
female
--ex. Male has chromosome for hair color/
female has chromosome for hair color
2. Diploid (2 sets of chromosomes)
3.
a. Cell has both sets of homologous chromosomes
b. Represented by 2N (46 chromosomes)
--human somatic (body) cell is 2N
c. cell has 2 sets of genes with complete set of
chromosomes
Haploid (1 set of chromosome)
a. Cell has one set of chromosomes and 1 set of
genes
b. Represented by N (23 chromosomes)
--gametes (germ cell)
*sperm (N) 23 chromosomes
*egg (N) 23 chromosomes
*sperm/egg form zygote (46 chromosomes)
C. Meiosis
1. process of reduction and division
2. chromosome number is reduced in half by
separation of homologous chromosomes in a
diploid cell
3. 2 divisions
a. Meiosis I
b. Meiosis II
4. final cells (sperm or egg) are genetically
different from original cell
5. tetrad
a. 2 pairs of sister chromatids (4 chromos.)
6. crossing over
a. An exchange of genetic material producing
new genetic info
b. May occur when tetrads are formed
7. handout
D. Gamete formation
1. 4 cells formed called gametes
2. male has 4 sperm formed
3. female has 1 egg with 3 polar bodies
a. Polar bodies—no reproductive value,
absorbed into the body
E. Comparing Mitosis/Meiosis
1. Mitosis
a. Forms 2 genetically identical cells
b. Diploid cells (46) form 2 diploid daughter
cells
c. Replaces/repairs/healing of body cells
d. Asexual reproduction
2. Meiosis
a. Begins with diploid (2N) cell to produce 4 haploid (N)
cells
b. Haploid cells are genetically different from original
diploid cell
c. By crossing over new genetic material is made
d. For sexual reproduction
11-1 Work of Gregor Mendel
A. Genetics
1. scientific study of heredity
2. key to species differences
B. Gregor Mendel’s Peas
1. Monk trained in math/science
2 Cared for monastery garden
3. Peas are self-pollinators
a. Have stamen (male) to produce pollen and
pistils (female) to produce egg on same
plant
b. The pollen self-pollinates the egg on the
same plant
c. Offspring are identical to parent
d. Also called true-breeds or pure breeds
4. Mendel’s experiment
a. Removed stamen (left pistal) on plants
b. Removed pistal (left stamen) on plants
c. Manually dusted pollen from one plant
onto pistal of another plant—called crosspollination
d. Cross-pollinated offspring are genetically
different from parents
e. Also called hybrids
C. Genes and Dominance
1. trait
a. Specific characteristic
--seed color, plant height, seed shape,
pod color, etc.
2. genes
a. Chemical factors which determine traits
b. Have contrasting forms
3. alleles
a. Different forms of genes
--Seed color (trait or gene)
--yellow or green (alleles)
--hair color (trait/gene)
--brown, black, blonde (alleles)
4. Generations
a. Parent (P)—original parents
b. First Filial (F1)—offspring
c. Second Filial (F2)—offspring’s offspring
5. Conclusion of crossings
a. Biological inheritance determined by
factors passed from generation to
generation
b. Some alleles are dominant, some are
recessive (Principle of dominance)
--dominant traits will always be expressed
if either parent has the dominant trait
*represented by capital letter
--recessive traits will only be expressed if
both parents have recessive trait
*represented by lowercase letter
D. Segregation
1. occurs during meiosis
2. alleles are segregated (separated) so each
gamete receives only 1 copy of gene (Law of
Segregation)
11.2 Probability and Punnett Squares
A. Probability
1. Likelihood an event will occur
2. Past events have no bearing on future
events
3. coin flip—50% chance or 1:2 of getting
heads
4. Principle of Probability
a. How will alleles segregate?
b. Used to predict genetic crosses
Parent
alleles
segregate
across top
and side
Parent 2
B. Punnett Square
1. Prediction and comparison of genetic
variation resulting from a cross
2.
Parent 1
offspring
offspring
offspring
offspring
Gene
combination of
offspring inside
boxes
3. Trait--Use same letter type
--ex. Hair color = T or t
4. Alleles
a. Dominant represented by capital (T)
b. Recessive represented by lowercase (t)
5. Homozygous (true or pure breeds)
a. Homo-same
zygous—joined
b. Identical alleles
--TT (homozygous dominant)
--tt (homozygous recessive)
6. Heterozygous (hybrids)
a. Hetero—different
b. Different alleles
--Tt
7. Phenotype
a. Physical trait (what can be seen)
b. Red hair, blue eyes, tall, red rose
8. Genotype
a. Genetic makeup (allele combinations)
b. TT, Tt, tt
9. monohybrid cross
a. Compares 1 trait only
10. Example
Parent 1—heterozygous for tall (Tt)
Parent 2—heterozygous for tall (Tt)
dominant—tall (T) recessive –short (t)
Parent 1
Parent 2
t
T
T
t
Offspring 1- Phenotype--tall
Homozygous tall
-Genotype--TT
TT
Tt
Offspring 2 and 3
-Phenotype—tall
Tt
tt
Heterozygous tall
-genotype—Tt
Offspring 4
-Phenotype—short
Ratios:
Homozygous short
Phenotype—3 tall, 1 short
-genotype—tt
3:1
Genotype– TT--1, Tt—2, tt—1
1:2:1
C. Probabilities Predict Averages
1. Predicts outcomes of large # of events
2. Larger the # of offspring the closer to
expected values (prediction of Punnett
Square)
3. 100 offspring would expect to see close to a
a. 3:1 phenotype ratio or 75:25 actual #’s
b. 1:2:1 genotype ratio or 25:50:25 actual #’s
4. 1000 offspring would be?
a. 3:1 or 750:250 (phenotype)
b. 1:2:1 or 250:500:250 (genotype)
5. Sometimes expressed as percentages not
ratios
a. 75% tall; 25% short (phenotype)
b. 25% TT; 50% Tt; 25% tt (genotype)
11-3 Exploring Mendelian Genetics
A. Independent Assortment
1. Alleles and genes segregate independently of each
other
a. They do not influence each other
b. Example: blonde hair/blue eyes do not always
appear together
2. Principle of Independent Assortment
a. Genes for different traits can segregate
independently during gamete formation
(Meiosis)
b. Accounts for genetic variation of organisms
3. Dihybrid cross
a. Use a two-factor (trait) cross (4 alleles)
b. Example:
--2 different traits/4 alleles
*seed shape—round or wrinkled,
*seed color—yellow or green
4.
Parents are round, yellow seeds (RrYy)
(1234)
a. Alleles segregate as follows
(1234) 1,3 1,4 2,3 2,4
RrYy RY Ry rY
ry
(1,3) RY
(1,3)
RY
(2,4)
ry
(2,4) ry
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
(1,4) Ry
(2,3) rY
(1,4) Ry (2,3) rY
B. Summary of Mendel’s Principle
1. Inheritance is determined by genes
2. Some genes are dominant, some
recessive
3. Adults have 2 copies of genes from
inheritance. Segregation of genes occur
during meiosis
4. Alleles for different genes segregate
independently.
C. Beyond Dominance and Recessive Alleles
1. Some genes are not dominant nor
recessive.
2. Many traits controlled by multiple alleles
or genes
3. Incomplete dominance
a. Neither allele is dominant,
heterozygous phenotype falls between
homozygous phenotypes.
--red 4 o'clock and white 4 o'clock
produces pink 4 o'clock
4. Codominance (form of incomplete dom.)
a. Both alleles contribute to phenotype
b. Red hair cattle/white hair cattle produce
a roan (pinkish-brown due to hair
combinations)
c. Can see red/white hairs
d. Chickens w/ black/white feathers
5. Multiple alleles
a. Genes have more than 2 alleles
b. Individual may inherit 2 alleles only
c. Blood types have alleles A,B,O
--combination can be
AA, AO, BB, BO, AB, OO
d. Eye color/hair color
6. Polygenic traits
a. Inheritance of several genes
--skin color (4 different genes)
--foot size
--nose length
--height
D. Applying Mendel’s Principles
1. Applies to all living organisms
2. Fruit fly is model organism for genetics
experiments (discovered by Morgan) b/c
a. Fly is small –easy lab storage
b. Quick reproduction
c. Quick life cycle (28 days)
E. Genetics and the Environment
1. characteristics are determined by the
interactions between genes and
environment
a. Plant height determined by genes but
genes may be affected by climate,
soil conditions, and water availability
11-5 Linkage and Gene Maps
A. Gene linkage
1. Some genes are almost always inherited
together and rarely become separate
2. Genes a linked and called linkage groups
3. The linked groups assort independently
but genes on linkage groups are
inherited together
4. Chromosomes assort independently not
the genes
B. Gene Maps
1. genes are located on chromosomes
2. farther apart on chromosomes more likely
genes will be separated during crossing over
3. gene maps show location on chromosome
4. human genome
a. Gene map of human chromosome
b. Can pinpoint hair color, diseases
such as cancer, mutations such as
Down’s, or anything determined by
genes