Study of heredity

1
Study of heredity
2

• Heredity passing of traits from parent to child
• Patterns of relatedness can help predict
  offspring characteristics

3
Chromosomes and Genes

• Genes are located on chromosomes
• Genes inherited from mom and dad
• Genes come in several forms called alleles

4
Chromosomes and Genes

• Allele Alternative forms of a gene
• Ex Flower color
• White allele or Purple allele

5

• An allele is any alternative form of a gene
  occurring at a specific locus on a chromosome.

• Each parent donates one allele for every gene.
• Homozygous describes two alleles that are the
  same at a specific locus.
• Heterozygous describes two alleles that are
  different at a specific locus.

6
Alleles can be represented using letters. Ex Aa
or AA or aa

• A dominant allele is expressed as a phenotype
  when at least one allele is dominant.
• A recessive allele is expressed as a phenotype
  only when two copies are present.
• Dominant alleles are represented by UPPERCASE
  letters
• Recessive alleles by lowercase letters.

7

• Dominant and Recessive Genes
• Gene that prevents the other gene from showing
  dominant
• Gene that does NOT show even though it is
  present recessive
• Symbol Dominant gene upper case letter T
• Recessive gene lower case
  letter t

Recessive color
Dominant color
8
Genotype and Phenotype

• Combination of genes an organism has (actual gene
  makeup) GENOTYPE
• Ex TT, Tt, tt
• Physical appearance resulting from gene make-up
  PHENOTYPE
• Ex hitchhikers thumb or straight thumb

9
Genetics Vocabulary Review

• Choices
• YY
• Tall
• Yy
• SS
• yY
• gg
• Smooth
• Green
• TT
• Dwarf

• Which choice(s) are examples of
• Genotypes?
• 1, 3, 4, 5, 6, 9
• Phenotypes?
• 2, 7, 8, 10
• Homozygous genotypes?
• 1, 4, 6, 9
• Heterozygous genotypes?
• 3, 5
• Homozygous recessive genotypes?
• 6
• Homozygous dominant genotypes?
• 1, 4, 9

10
Dominant vs. Recessive
1

• If Brown eye color is dominant over blue eye
  color, how would you indicate
• The brown allele?
• The blue allele?

11
Dominant vs. Recessive
2

• If dimples in the cheeks are dominant, how would
  you indicate
• The allele for dimples?
• The allele for no dimples?

12
Dominant vs. Recessive
3

• If left thumb over right thumb is dominant, how
  would you indicate
• Left over right?
• Right over left?

13
Mendel laid the groundwork for genetics.

• Traits are distinguishing characteristics that
  are inherited.
• Genetics is the study of biological inheritance
  patterns and variation.
• Gregor Mendel showed that traits are inherited as
  discrete units.
• Many in Mendels day thought traits were blended.

14
Mendels data revealed patterns of inheritance.

• Mendel made three key decisions in his
  experiments.
• use of purebred plants
• control over breeding
• observation of seveneither-or traits

15

• Mendel used pollen to fertilize selected pea
  plants.

• P generation crossed to produce F1 generation
• interrupted the self-pollination process by
  removing male flower parts

16

• Mendel allowed the resulting plants to
  self-pollinate.

• Among the F1 generation, all plants had purple
  flowers
• F1 plants are all heterozygous
• Among the F2 generation, some plants had purple
  flowers and some had white

17
Genetic Vocabulary

• Generations
• P parental generation
• F1 1st filial generation, progeny of the P
  generation
• F2 2nd filial generation, progeny of the F1
  generation (F3 and so on)
• Crosses
• Monohybrid cross cross of two different
  true-breeding strains (homozygotes) that differ
  in a single trait.
• Dihybrid cross cross of two different
  true-breeding strains (homozygotes) that differ
  in two traits.

18
Each trait had a 31 ratio. No way that can be a
coincidence!
19
Mendels 3 Conclusions

• 1. Law of Dominance
• If the two alleles of a particular gene present
  in an individual are the same, the individual is
  said to be homozygous. (dominant or recessive)
• If the alleles of a particular gene present in an
  individual are different, the individual is
  heterozygous.
• In heterozygous individuals, only the dominant
  allele is expressed the recessive allele is
  present but unexpressed.

20
Mendels 3 Conclusions

• 2. Traits are inherited as discrete units.
• Organisms inherit two copies of each gene
  (allele), one from each parent.
• Genes are inherited independently of each other.

21
Mendels 3 Conclusions

• 3. Law of Segregation
• The two copies of alleles segregate during gamete
  formation.

22

• Defined Tools used to determine genetic
  probability
• Probability likelihood that a certain event
  will happen
• 2 Steps
• 1) Place parent genotypes on the outside of the
  box
• 2) Fill in the boxes

Punnett Squares
23

• Cross a homozygous dominant yellow (YY) plant
  with a homozygous recessive green (yy) plant

y y
y
y
y
y
Key Y yellow y green
Y Y
100
Probability of growing a yellow plant?
_____________
0
Probability of growing a homozygous recessive
plant? ____________
0
Probability of growing a homozygous dominant
plant? ____________
24

• Cross a heterozygous dominant yellow (Yy) plant
  with a heterozygous dominant yellow (Yy) plant

Y
Y
Y
y
y
y
Y
Y
Y
Key Y Yellow y green
y
y
y
50
Probability of growing a heterozygous plant?
________
25
Probability of growing a green plant? ________
25
Probability of growing pure yellow? _________
25
Maria is a heterozygous healthy (Hh) female and
Jeff suffers from recessive cystic fibrosis (hh).
h
h
h
h
h
h
Key H healthy h cystic fibrosis
H
H
H
h
h
h
Probability of having a healthy child? _________
Probability of having a homozygous dominant
child? ________
50
0