Finals B

Mendel's Theory of Inheritance

Mendel was an Austrian monk in 1860's who studied inheritance patterns of simple traits in the garden pea.

Phenotype

The visible type of a trait.

Alleles

Different forms of a gene that determine distinct traits.

Dominant allele

Masks the presence of a recessive allele; need only one copy to see the dominant phenotype.

Recessive allele

Need 2 copies of a recessive allele to see the recessive phenotype.

Genotype

The combination of alleles on the chromosomes.

Law of Segregation

Each organism is diploid and has 2 copies of each gene; during Meiosis, these alleles segregate so that each gamete contains only one allele for each gene.

Homozygous

An organism has 2 of the same alleles.

Heterozygous

An organism has 2 different alleles.

Dominant Phenotype

The phenotype expressed when at least one dominant allele is present.

Monohybrid Cross

A genetic cross that studies the inheritance of one trait.

Phenotypic ratio

The ratio of different phenotypes in the offspring; for example, 3 Purple: 1 white.

Genotypic ratio

The ratio of different genotypes in the offspring; for example, 1 PP: 2 Pp: 1 pp.

Truebreeding

Organisms that are homozygous for a trait and produce offspring with the same phenotype.

F1 generation

The first generation of offspring from a genetic cross.

F2 generation

The second generation of offspring, produced by self-pollinating the F1 generation.

Punnett Square

A diagram used to predict the genotype and phenotype combinations of a genetic cross.

Freckles

A trait determined by the allele F (freckles) and f (no freckles).

Gametes

Reproductive cells that carry alleles from each parent.

Self-pollinate

The process by which a plant fertilizes itself.

PP

Homozygous dominant genotype for purple flowers.

pp

Homozygous recessive genotype for white flowers.

Pp

Heterozygous genotype for purple flowers.

F

freckles

f

no freckles

Genotypic ratio

the number of offspring with each genotype

Phenotypic ratio

the number of offspring with each phenotype (outward appearance)

Genotype with Freckles

FF and Ff

Genotype with No freckles

ff

Phenotypic ratio for freckles

3 Freckles: 1 no freckles

% of children with Freckles from Ff x Ff

75% Freckles and 25% no freckles

Testcross

cross an organism with the dominant phenotype with an organism with the recessive phenotype.

Gametes of dominant parent

T and ?

Gametes of recessive parent

only t

Expected phenotypic ratio from Tt x tt

1 Tall: 1 short

Expected phenotypic ratio from TT x tt

all Tall (and no short!)

Offspring from TT x tt

expect all Tall = Tt

Offspring from Tt x tt

Expect 1/2 Tall & 1/2 short

Tall parent genotype from 3 Tall and 1 short offspring

Tt X tt

Tall parent genotype if no short offspring

TT

Green pod color dominance

green pod color is dominant over yellow pod color.

Heterozygote cross with yellow pod plant

what percent of the offspring will have yellow pods?

Purple flowers dominance

purple flowers are dominant over white flowers.

Phenotypic ratio of offspring from purple and white flower cross

48 plants have purple flowers and 52 plants have white flowers.

Genotype of the Purple parent

unknown without further information.

Genotype of the white parent

unknown without further information.

Dihybrid Cross

The inheritance of 2 traits is studied.

Seed Color

Yellow (Y) or green (y).

Seed Shape

Round (R) or wrinkled (r).

Law of Independent Assortment

The inheritance of one trait is independent of the inheritance of another trait (assume the genes are not linked).

Parental Cross

YYRR X yyrr.

Gametes from YYRR parent

Can make only YR gametes.

Gametes from yyrr parent

Can only make yr gametes.

Gametes requirement

Gametes must have 1 Y allele (Y or y) AND 1 R allele (R or r).

Punnett Square

Do the Punnett Square to determine the genotypes and phenotypes of the offspring.

Phenotypic Ratio of YyRr x YyRr

9 Yellow Round (YR), 3 Yellow wrinkled (Yrr), 3 green Round (yyR), 1 green wrinkled (yyrr).

Monohybrid Cross

A cross between 2 heterozygotes produces a 3:1 ratio.

Phenotypic Ratio for Yy x Yy

3 Y_: 1 yy.

Phenotypic Ratio for Rr x Rr

3 R_: 1 rr.

Dihybrid Cross Splitting

A Dihybrid Cross can be split into 2 monohybrid crosses.

Dihybrid Cross Problems

Do the problems on the worksheet called Dihybrid Cross Lecture Problems.

Phenotypic Ratio of Heterozygote Cross

Green pod, Purple: Green pod white: yellow pod Purple: yellow pod white.

Genotypes of Heterozygote for Both Traits

Heterozygote for both traits = yellow pod and homozygous dominant flower color.

Genotypes of Parents for Pumpkins

Round, warty pumpkin = ?; oval, smooth pumpkin = ?.

Phenotypic Ratio of Offspring for Pumpkins

What is the phenotypic ratio of the offspring?

Making All Squares Smooth

How can you make all of the squares Smooth?

Making Half Squares Round and Half Oval

How can you make half the squares Round and half oval?

Autosomal Genetic Disorders

Medical conditions inherited from either parent that may be dominant or recessive.

Huntington disease

A dominant autosomal disorder that develops severe neurological problems and eventual death, typically onset at age 40 or older.

Achondroplasia

A dominant disorder that is a common form of dwarfism characterized by shortened limbs and short stature.

Cystic fibrosis

An autosomal recessive disease caused by a defective Cl transport protein, leading to thick mucus in lungs and digestive tract.

Tay Sachs

An autosomal recessive disease caused by a missing lysosomal enzyme, resulting in neurological problems and death by age 5.

Sickle Cell Anemia

A disease caused by a point mutation in the gene for hemoglobin, leading to sickled red blood cells, poor circulation, and anemia.

Pleiotropy

A phenomenon where one gene influences multiple phenotypic traits, as seen in cystic fibrosis.

Dominant Disease

A genetic disorder that manifests when at least one dominant allele is present.

Recessive Diseases

Genetic disorders that manifest only when an individual has two recessive alleles.

Modified Mendelian Inheritance

Inheritance patterns that deviate from Mendel's laws, including incomplete dominance.

Incomplete Dominance

A genetic scenario where the phenotype of the heterozygote is a blending of the dominant and recessive traits.

Complete Dominance

A genetic scenario where the phenotype of the heterozygote is the same as that of the dominant homozygote.

Balanced Polymorphism

A situation where two or more phenotypes are maintained in a population due to selective advantages, such as sickle cell trait providing malaria resistance.

HH

Homozygous dominant genotype for Huntington's disease.

Hh

Heterozygous genotype for Huntington's disease, exhibiting the disease phenotype.

hh

Homozygous recessive genotype for Huntington's disease, exhibiting normal phenotype.

Aa

Heterozygous genotype for achondroplasia, resulting in dwarfism.

aa

Homozygous recessive genotype for achondroplasia, resulting in normal height.

AA

Homozygous dominant genotype for achondroplasia, which is lethal.

HbA

Normal hemoglobin allele.

HbS

Sickle cell allele.

RBC

Red blood cell, which can have a sickled shape in sickle cell anemia.

Peter Dinklage

An actor known for portraying Tyrion Lannister in Game of Thrones, who has achondroplasia.

Incomplete Dominance

Occurs when the heterozygote is intermediate between the 2 homozygotes.

Genotypic Ratio of Incomplete Dominance

1 CRCR, 2 CRCw, 1 CwCw.

Phenotypic Ratio of Incomplete Dominance

1 CRCR = Red, 2 CRCw = Pink, 1 CwCw = White.

Familial Hypercholesterolemia

Caused by defective receptor for LDL cholesterol -> cells can't take up LDL from the blood.

LDL Receptor Genotypes

HH: normal LDL receptors, Hh: high levels of LDL cholesterol, hh: extremely high levels of LDL cholesterol.

Serum Cholesterol Levels

HH: 130-260 mg/100 ml, Hh: 250-500 mg/100 ml, hh: 650-1000 mg/100 ml.

Cholesterol Levels Recommendation

Cholesterol levels should be below 200.

Cardiovascular Disease

Presence of excessive cholesterol causes Cardiovascular disease.

Gene for Hair Curl

HC allele: curly hair, HS allele: straight hair.

Example of Incomplete Dominance in Hair Curl

HCHC (curly hair) x HSHS (straight hair) -> HCHS (wavy hair).