Bio 2.9 Exam

Heredity

Transmission of traits from one generation to the next

-Gregor Mendel (monk 1860s)

Genetics

Study of heredity

Character

Heritable feature that varies among individuals

Traits

Variant of a character

Why did Gregor Mendel use pea plants?

They could easily be controlled by reproduction (self-fertilize)

Hybrid

Offspring of two pure breads

P generation is…

the purebread

Hybrid offspring

F1

Offspring of that F1

F2

Mendel’s Four Hypothesis

1) Alleles-alternative versions of A SAME gene

2) homozygous,heterozygous

3)dominant,recessive

4)Law of segregation

Law of Segregation

Individual has two alleles for a trait,and these seperate during gamete formation, so each gamete only gets one allele

• Anaphase l of meiosis

• Separation of alleles for one trait

Law of Independent Assortment

Alleles of different genes separate independently of one another;genes on different chromosomes

• Metaphase l meiosis

• Random combo of alleles for different traits

• Explains ratios

Testcross

Cross unknown genotype with a homozygous recessive organism

Alleles

Different version of a gene

Why does the law of segregation explain how genes are transmitted from one generation to the next?

Because genes are located on homologous chromosomes at specific loci, and during meiosis the two alleles seperate (segregate). Each gamete receives only one allele,so gene transmission follows this separation.

Family tree

Pedigree

What does Male in a pedigree represent?

A square

What does female in a pedigree represent?

A circle

Shaded/Unshaded in pedigree?

• Shaded means that the trait is shown

-Unshaded means the trait is not shown

Wild type

Traits most common in nature

:Straight hairline

:Normal color vision

:Normal hemoglobin

Widows peak and Freckles are…

Dominant

Straight hair is…

Recessive

Recessive Disorders

-Born to normal parents who are heterozygous: Aa x Aa

-person is homozygous: aa

-Albinism

-Cystic fibrosis:excess mucus in lungs,digestive tracts and liver (most common 1 in 31 Americans)

-PKU: phenalyaline in blood lack normal skin

-Sickle cell:misshaped red blood

-Tay Sachs: Lipid accumulation in brain cells;

Dominant Disorders

Parents: Aa (affected) x aa (normal)

Those affected has an Aa genotype

-Achondroplasia-Dwarfism

-Alzheimer’s

-Huntington’s disease-uncontrollable movements, middle age,cognitive,impair

-Hypercholesterolemia: excess cholesterol in blood,heart disease

• Dominant alleles that cause these disorders are LESS common than Recessive

Most to least common blood types?

Type O: 63%

Type A: 21%

Type B: 16%

Genetic Testing in the past… Genetic test now

Onset of symptoms was the only way to know if a person has inherited genetic disease

• Modern tech can help identify 30 treatable genetic disease

What is amniocentesis?

A prenatal test where a small amount of amniotic fluid is removed with a needle through the abdomen. The fluid contains fetal cells that can be tested for chromosomal and genetic disorders.

What is chorionic villus sampling (CVS)

A prenatal test where a sample of a placental tissue (chronic villi) is removed through the cervix or abdomen. Tests fetal chromosomes and genes.

What are prenatal tests?

Medical tests done during pregnancy to check the health,development,and genetic status of a fetus.

Incomplete Dominance

F1 hybrid falls between the phenotypes of two parents

ABO blood types

Involve three alleles of a single gene and produce 4 genotypes

A,B,AB,or O.

Type A

• I^A I^A-homo

• I^A i-hetero

Type B

• I^B I^B-homo

• I^B i-hetero

Type AB

I^A I^B

Type O

ii

What do the A and B letters in blood types refer to?

They refer to carbohydrate antigens (A and B) on the surface of red blood cells

What does the positive or negative (Rh factor) in blood type mean?

It refers to the Rh blood group system,controlled by a seperate, unrelated gene.

-There are about 50 different Rh alleles

Why is AB+ the universal red blood cell recipient?

-Because AB+ has all antigens (A,B,Rh) and therefore no anti-A,anti-B, or anti-Rh antibodies.

Why is O- the universal red blood cell donor?

Because O- has NO A, no B, and no Rh antigens,so it will not trigger an antibody reaction in any recipient

Pleiotropy

One single gene affects multiple traits in the body

Effect:mutation in one gene can cause different symptoms or changes in multiple systems

Polygenic

A trait is controlled by MANY genes

Effect:Each gene contributes a little bit, so the trait shows a range of possibilities,not just one or two forms.

Variation of genes

Diabetes,heart disease,and cancer are polygenic

Height,skin color,eye color are also polygenic

-Environmental factors

Some features are…

determined by environment,some by both

Heart disease,cancer, alcoholism ,schizophrenia is influenced by both genes and environment

What is epigenetic inheritance?

The transmission of traits or gene expression patterns without changing the DNA sequence itself.

How does epigenetic inheritance work?

Chemical groups are added to or removed from DNA or its proteins, altering how genes are expressed without changing the DNA bases

What influences epigenetic changes?

Environmental factors such as diet,stress,toxins,and lifestyle can modify gene expression.

How does epigenetics explain differences between identical twins?

Even with identical DNA,environmental differences can change gene expression, so one twin may develop a genetically linked disease while the other does not.

Who can receive what?

AB—>AB

A—> A,AB

B—> B,AB

O—> O,A,B,AB

Golden blood only golden blood

What is the Chromosomal Theory of Inheritance?

Genes are located at specific positions (loci) on chromosomes. They undergo segregation and independent assortment during meiosis explaining how traits are inherited.

What happens when genes are near each other on the same chromosome?

They are linked genes, which travel together during meiosis and fertilization, disobeying Mendel’s law of independent assortment

How are sex chromosomes distributed in humans?

Males=XY

Females=XX

-Segregation during meiosis produces 4 gametes:each with sex chromosome and a haploid set of autosomes

(22 in humans)

—All eggs contain X, sperm are half X, half Y—> father determines sex

How many genes are on human X and Y chromosomes?

X-1,1000 genes

Y-78 genes

Most sex-linked genes are on the X chromosome

Examples of X-linked recessive disorders?

Red-green color blindness,hemophilia,and muscular dystrophy.

Why does sex determination depend on the father?

All eggs carry an X chromosome,while sperm carry X or Y. The sperm’s sex chromosome determines the offspring’s sex.

Red-green color blindness

Common sex-linked disorder that is caused by malfunction of light sensitive cells.

Normal Vision vs Colorblindness

150 colors normal

25 colors blindness

Why are men more affected by red-green colorblindness?

Because it is X-linked resessive, and males have only one X chromosome. A single recessive allele on that X causes the trait, while females need two recessive alleles to be affected.

Genotypes for eyesight

N-normal vision

n—color blind

Male: XY

Normal vision

X^N Y

Color blind

X^n Y

Female:XX

X^N X^N-normal

X^N X^n-carrier,normal

X^n X^n-color blind

What is hemophilia?

A sex-linked recessive trait with a long history. Hemophiliacs bleed excessively when injured because they inherited an abnormal allele for a factor involved in blood clotting. Many bleed to death after minor bruises or cuts.

Queen Victoria-Carrier of hemophilia