Chapter 7 Genetics

Gregor Johann Mendel

1) Austrian Monk 2) Bred pea plants and observed their outcomes 3) He discovered patterns of inheritance that now form the current study of genetics

Mendel's theory of Hereidty

1) There are different versions of genes. 2) When two different alleles are inherited together, one may be expressed, while the effect of the other may be silenced. 3) For each characteristic, an organism inherits two alleles, one from each parent. 4) When gametes are formed, the two alleles of each gene are separated.

The Principle of Dominance

1) one gene in a pair masks the other from being expressed

7 main characteristics Mendel studied

1) seed texture (round or wrinkled) 2) seed color ( yellow or green) 3) seed coat color (white or colored) 4) pod appearance (inflated or constricted) 5) pod color (yellow or green) 6) position of flowers (axial or terminal) 7) plant height (tall or short)

Why did Mendel use pea plants in his studies?

1) several observable traits 2) both male and female parts 3) it grows quickly

A flower exhibits incomplete dominance. If one flower is red and one is white, what is the probability of their offspring becoming pink?

100% *All pink

P x P

F1

The results of a cross of the parental generation.

F1

What did Mendel call the offspring of the P generation?

F1 (1st Filial generation)

F1 x F1

F2 (2nd Filial Generation)

A cross in which the phenotype is a blend or is in between the two alleles

Incomplete Dominance

A cross between organisms involving only one trait

Monohybrid Cross

How do the Punnett squares for a monohybrid cross and a dihybrid cross differ?

Monohybrid: involves only one trait Dihybrid: involves two traits

Traits determined by two or more alleles.

Multiple alleles

_____ _____ are responsible for traits such as hair color, eye color, height, and weight

Multiple alleles

A classmate tells you that a person can have a type AO blood. Do you agree? Explain?

No, AO blood type is not possible

Blue eyes (b) is recessive to brown (B) eyes. Cross a heterozygous brown-eyed dog with a blue-eyed dog. What are the resulting genotypic and phenotypic ratios?

P ---> 2:2 G ---> 0:2:2

Tall (T) is dominant over short (t) in corn. Cross a homozygous tall plant with another plant of the same genotype. What are the resulting genotypic and phenotypic ratios?

P ---> 4:0 G ---> 4:0:0

The letters outside the boxes in a Punnett square represent _____ _____.

Parents' alleles

An observable trait - what you see

Phenotype

When two or more genes affect a trait

Polygenic Inheritance

The fraction or percentage that describes the likelihood of an event occurring.

Probability

A diagram that shows possible outcomes of a genetic cross

Punnett Square

Pedigree that skips a generation (one generation missing affected)

Recessive

The allele in a pair that does not affect the trait

Recessive

The sex linked allele is located on the __ _____.

X chromosome

Non-carrier Female

X^H X^H

Carrier Female

X^H X^h

Normal Male

X^H Y

Female with hemophilia

X^h X^h

Male with Hemophilia

X^h Y

Is it sometimes possible to tell a person's genotype by their phenotype?

Yes

A sample of peas contains 600 green peas and 200 yellow peas. a) what proportion of peas are green? b) What is the ratio of green to yellow peas?

a) 3/4 b) 3/1

Law of Independent Assortment

alleles of different genes separate independently of one another during gamete formation

Genotype

an organism's genetic make-up ex. BB, Bb, bb

Phenotype

an organism's physical appearance ex. brown eyes

autosome

any chromosome of that a sex chromosome

Universal donor

can donate blood to anyone (Type O)

Universale acceptor

can receive blood from anyone (Type AB)

Sex-linked traits

carried on the X chromosome *usually RECESSIVE - effects usually only seen in males

sex chromosome

chromosome that determines the sex of an organism

hybridization

cross between two individuals that have different traits

testcross

determine the organism's genotype

Heterozygous

different alleles for each trait

Alleles

different forms of a gene; come from your parents; different alleles for each zygote

Trait

heritable variant of a genetic character

Codominance

heterozygous offspring express BOTH phenotypes of the parents

In order for a recessive trait to be expressed, the genotype must be _____ recessive.

homozygous

Type O

ii

Monohybrid Cross

involves only one trait

Dihybrid Cross

involves two traits

Genes

located on chromosomes

Sex-linked disorders occur more commonly in _____.

males

True-breeding

organisms that are pure for a trait

Cross-breeding

placing pollen from one pure plant onto the stigma of another pure plant

Hemophilia

sex-linked recessive trait *a defective gene reduced the blood's ability to clot properly

Dominant

the expressed gene - Capital letter

Recessive

the masked gene - lowercase letter

Homozygous

the same allele for a trait

Polygenic Inheritance

traits inherited from a combination of genes - several genes influence a trait - affect things such as height, eye color, skin color, hair color

Law of Segregation

two alleles for a trait segregate (separate) during gamete formation (meiosis)

Incomplete Dominance

when the F1 generation shows a phenotype in between that of the parents *Genotype is always heterozygous

The offspring exhibits both traits

Codominance

Parental generation

"P"

Pedigree

- only recessive traits can skip a generation - If homozygous dominant, ALL offspring will display the trait - If the trait skips a generation, both parents are heterozygous

If having brown eyes is dominant, show how two parents with brown eyes could have children with blue eyes using a monohybrid cross. What are the odds (%) of this happening?

25%

Complete dihybrid cross with all traits heterozygous. Phenotypic ratio? ex. FfEe x FfEe

9:3:3:1

IF BOTH PARENTS ARE HETEROZYGOUS FOR BOTH TRAITS... PHENOTYPIC RATIO IS

9:3:3:1

The alternative forms of genes

Alleles

Blue (B) is dominant to white (b) in flowers. What is the genotype for a plant that is heterozygous? What would be its phenotype?

Bb P ---> Blue

_____ are heterozygous for a disorder, but do not exhibit the disorder

Carriers

A cross involving two traits rather than one

Dihybrid cross

In a heterozygous individual, what allele is expressed?

Dominant

Pedigree that has affected trait presented throughout

Dominant

The allele of the pair that seems to affect the trait. Shows up

Dominant

The study of heredity

Genetics

The genetic makeup of combination of alleles.

Genotype

Who is the "father of modern genetics?"

Gregor Johann Mendall

An individual with two alleles for a trait being different

Heterozygous

An individual with two alleles the same for a trait

Homozygous

The offspring of two different purebreds

Hybrid

Type AB

I^A I^B

Type B

I^B I^B or I^B i

Type A

I^a I^A or I^A i

Any gene located on the sex chromosomes.

Sex-linked trait

Which blood types are not possible for children of two parents with type AB blood?

Type O