Chapter 11 - Introduction to Genetics

Gregor Mendel Strong background in plant breeding and mathematics Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

Traits Specific characteristics that vary from one individual to another Determined by genes 7 traits studied by Mendel Seed shape and color, pod shape and color, position, height

Mendel’s Peas True Breeding Producing offspring with traits identical to parent Result of self-pollination of pea plants Hybrid Offspring that results from parents with different traits Result of cross-pollination

Genes Chemical factors that determine traits (units of information) Passed from parents to offspring Each has a specific location (locus) on a chromosome

Alleles Different forms of a gene Dominant allele (Uppercase letter) overrules a recessive allele (lowercase letter) that it is paired with

Principle of Dominance Some alleles are dominant and others are recessive Recessive allele must be present WITHOUT dominant allele, then recessive form of trait will be expressed

Allele Combinations Homozygous =purebred Heterozygous =hybrid having two identical alleles at a locus AA (dominant expressed) or aa (recessive expressed) Heterozygous =hybrid having two different alleles at a locus Aa (dominant expressed)

Segregation Separation of alleles during the formation of gametes (sperm and egg)

Tracking Generations Parental generation P mates to produce First-generation offspring F1 which mate to produce Second-generation offspring F2

Genotype & Phenotype Genotype refers to particular genes an individual carries (represented by letters) Phenotype refers to an individual’s physical/observable traits: actual expression of gene Cannot always determine genotype by observing phenotype…

What happens when a true breeding purple flower breeds with a true breeding white flower?

Figure 24–5 The Structure of a Flower Section 24-1 Filament Anther Stigma Style Ovary Carpel Petal Sepal Ovule Stamen

How did Mendel fertilize the plants?

Mendel’s Question Mendel wanted to know if the recessive alleles disappeared or are they still in the F1, just hidden.

Note differences between phenotype and genotype amongst different generations.

Dominant trait is expressed F M Dominant trait is expressed Recessive appears

The actual expression Type of alleles

Female Allele - different form of a gene Male

Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall

T T t t Principles of Dominance P Generation F1 Generation Tall Short Tall Tall Tall Tall Tall Short T T t t

T T t t T t T t Principles of Dominance P Generation F1 Generation Tall Short Tall Tall Tall Tall Tall Short T T t t T t T t

T T t t T t T t T T T t T t t t Principles of Dominance P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short T T t t T t T t T T T t T t t t

Tt X Tt Cross

What are the phenotypic and genotypic ratios? Tt X Tt Cross What are the phenotypic and genotypic ratios?

Dominant & Recessive Alleles If you have attached earlobes, you inherited two copies of the recessive allele (ee) If you have detached earlobes, you may have either two or one copy of the dominant allele (EE or Ee)

Earlobe Variation Whether a person is born with attached or detached earlobes; depends on a single gene Gene has two forms (alleles)

Earlobe Variation You inherited one allele for this gene from each parent Dominant allele specifies detached earlobes (E) Recessive allele specifies attached earlobes (e)

Incomplete Dominance Neither allele is dominant over the other. Both alleles represented by uppercase letters (RW). Combination of red and white making a new phenotype (pink!)

Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

Codominance BOTH alleles are dominant (ex. Red flower and White flower made Red and White flower, not pink!) Blood Type A (IA) and Blood Type B (IB), when combined make Blood Type AB

Multiple Alleles Genes with more than 2 alleles Ex. With blood types there are 2 dominant alleles and 1 recessive IA=dominant Blood Type A IB=dominant Blood Type B i=recessive Blood Type O

Figure 14-4 Blood Groups (Pg. 344-345) Safe Transfusions Phenotype (Blood Type Antigen on Red Blood Cell Genotype To From

ABO Blood Type: Allele Combinations Phenotypes: Genotypes: Type A - IAIA or IAi Type B - IBIB or IBi Type AB - IAIB Type O - ii

Universal Acceptor Universal Donor

What percentages of offspring do you get from a mother with blood type AB and a father with blood type O? IAIB x i i i i IA IB

What percentages of offspring do you get from a mother with blood type AB and a father with blood type O? IAIB x i i i i IA IAi IAi IB IBi IBi

Genetic Problem - Blood Types A man with A blood and a woman with B blood have a child. What are the chances of their child having having B blood if they are both heterozygous? What are their chances of having three children with O blood?

Rh factor - Another Blood Trait Rh+ is dominant What happens when Rh- mother is impregnated by Rh+ father? Baby is Rh+ and mother becomes sensitized after first birth Mother then creates antibodies to fight Rh+ blood Further Pregnancy complications

Polygenic Traits More than one gene controls a trait Skin color more than one gene, incomplete dominance Bell Curve-used to represent frequency of polygenic traits

A, B, and C are dark a, b, and c are light