Bio Quiz 2

Quiz 2 - Spermatogenis - Oogenesis - Errors during Meiosis - Mendelian Genetics - Monohybrid Crosses - Dihybrid Crosses - missing last lesson will

Gametogenesis

gamete formation

Spermatogenesis

production of sperm

• meiosis takes place in testes

• begins with diploid sell called a spermatogonium

Oosgenesis

production of eggs

• meiosis takes place in the ovaries

• begins with a diploid cell called an oogonium

• Ogonia reproduces by mitosis, then begin meiosis but stops at purchase 1 till meiosis 1 continues for the cell each month beginning at puberty. Creating an unequal division of cytoplasm (a polar body and a visible egg)

Gamete formation in animals

• Meiosis in mammals differs drastically between males & females

• two types of ____________ in humans

  • Spermatogenesis

  • Oogenesis

Spermatogonium (pl: Spermatogonia)

• a diploid that starts spermatogenesis

• _____________ reproduces by mitosis and resulting cells undergo meiosis

• 1 _____________ produces 4 sperm

Oogonium (pl: Oogonia)

• a diploid cell that starts oogenesis

• _________ reproduces by mitosis, then begins meiosis but stops at prophase 1

Polar Body

created during oogenesis and will eventually degenerate

Major differences between Spermatogenesis & Oogenesis

• cytokinesis is unequal among daughter cells during __________

• at birth, the ovaries contain all the cells it will ever have that will develop into eggs

  • sperm continue to develop by meiosis throughout the male reproductive years

• __________ has a long resting period after prophase 1 until hormones activate them

Why is cytokinesis is unequal during oogenesis

• ensures only one zygote is formed during fertilization

• more nutrients given to 1 egg to ensure survival or zygote

• more than one zygote means nutrients are divided (increases chance of health complications)

400,000 - 500,000 eggs

• all the cells in the ovaries that will ever develop into eggs

• only 400 will mature and become eggs

• each egg will complete division process upon puberty one at a time

Fraternal Twins

When more than 1 egg is released and both are fertilized (diff DNA)

Identical Twins

A single zygote divides into two separate bodies (genetically identical)

Importance of Meiosis

provides a vast amount of genetic variation

Independent Assortment

How pairs orient themselves in Metaphase1 and Metaphase2 will determine their variance (diff combos of chromosomes). In Anaphase1 homologs pairs independently separate, in Anaphase2 sister chromatids independently separate.

• 2ⁿ

2ⁿ

• number of genetically distinct gametes that can be produced from a diploid cell during independent assortment

• n = number of chromosome pairs

• In humans 2²³ = 8,388,608

Crossing Over

In prophase1 chromosomes exchange DNA by ________ each other

• occurs in several points along non-sister chromatids

• result: chromosomes have genes form maternal & paternal origin

• bonds holding DNA together are broken & reformed (might not reform correctly)

Errors Cause by Changes in Chromosome Structure

Deletion, Duplication, Inversion & Translocation

Deletion

• a piece of the chromosome deleted/lost

• missing gene = info form making vital proteins missing

• can be caused by: viruses, irradiation, chemicals

Cri du Chat Syndrome

• example of deletion

• rare genetic disorder due to missing part of chromosome 5 symptoms include unusual facial features

Prader-Willi Syndrome

deletion in chromosome 15

Duplication

a section of a chromosome appears two or more times in a row, some repeats are okay but too many can affect the function of the gene

Fragile X Syndrome

example of duplication when a singe nucleotide sequence (CCG) repeats on the X chromosome

Inversion

a certain gene segment becomes free from its chromosome momentarily before being reinserted in the reverse order. Changes the position and order of chromosome genes and can alter gene activity.

Translocation

part of one chromosome changes places with another part of the same chromosome pr with part of another, non-homologous chromosome.

Translocation Down Syndrome (Trisomy 21 Down Syndrome)

_______________ can be caused by a translocation between chromosomes 14 and 21. Only form of this syndrome that can sometimes be inherited from a parent.

Errors Caused by Changes in Chromosome Number

Non-disjunction

When homologous chromosomes don’t separate during meiosis. Can be during Anaphase1 or Anaphase 2 (sister chromatids don’t separation)

result: one sell has too many chromosomes and one has too little

Down Syndrome as Trisomy

Instead of 46 chromosome, a person with _________ has 47. An additional chromosome is added to the 21st pair.

Trisomy

3 chromosomes

Gregor Mendel (1822-1884)

• Austrian monk who studied the inheritance of traits in pea plants and developed the laws of inheritance. Work wasn’t recognized until the turn of the 20th century.

• 1856-1863, cultivated and tested some 28,000 pea plants and found that the plants' offspring retained traits of the parents

• Called the “Father of Genetics"

Particulate Inheritance

Mendel stated that physical traits are inherited as “particles” not knowing the the “particles” were actually DNA

Trait

any characteristic that can be passed from parent to offspring (based on two genes, one from mom & one from dad)

Heredity

passing of traits from parent to offspring

Genetics

study of heredity

monohybrid cross

cross involving a single trait (tracks the inheritance of one trait) and predicts the “probability of the traits that resulting offspring will have

dihybrid cross

cross involving two traits (track inheritance of two traits) and predicts the probability of the traits that the resulting offspring will have.

Alleles

two forms of a gene (dominant & recessive)

Dominant

stronger of two genes expressed in the hybrid; represented by a capital letter (R)

Recessive

gene that shows up less often in a cross; represented by lower case letter (r)

Genotype

gene combo for a trait (ex. RR, Rr, rr)

Phenotype

physical feature resulting from a genotype (ex. red, white)

Homozygous genotype

gene combo involving 2 dominant or 2 recessive genes AKA pure

Heterozygous genotype

gene combo of one dominant & one recessive allele AKA hybrid

Characteristics

determined by genes and environment

Why did Mendel Choose Peas

• Can be grown in a small area 

• Produce lots of offspring 

• Produce pure plants when allowed to self-pollinate several generations 

• Can be artificially cross-pollinated 

How Mendel Started

produced pure strains by allowing the plants to self-pollinate for several generations

Parental (P₁) Generation

the _____________ gen in a breeding experiment

F₁ Generation

first-gen offspring’s (first filial gen) from breeding individuals from P₁ gen

F₂ Generation

second-gen offspring’s (second filial gen) from breeding individuals from F₁ gen

3:1

Ratio of Recessive & Dom genes (phenotypic ratio)

What are the results of

RR x rr

R = round

r = wrinkled

Genotype: all Rr

Phenotype: all round

Homozygous dominant x Homozygous recessive

all ofspring’s are heterozygous

Heterozygous x Heterozygous

Offspring:
25% Homozygous dominant RR
50% Heterozygous Rr
25% Homozygous Recessive rr

1:2:1

Genotypic ratio of monohybrid cross

Test Cross

to determine an unknown genotype that is phonetically dominant

• if an individual appears phenotypically dom they can be either homozygous dominant or heterozygous

• use punnett square to figure out

True-Breeding

Individuals are homozygous (both alleles are the same)

3 Mendelian Laws

• law of dominance

• law of segregation

• law of independent assortment

5 ways of genetic variation

• Independent Assortment

• Crossing Over

• Errors in Chromosome Structure

• Errors in Chromosome Splitting (chromosome number)

• Errors in DNA replication

Law of Dominance

dominant trait is always expressed

RR x rr = Rr x 4 (only the R trait will be expressed)

Law of Segregation

during the formation of gametes, the two alleles for a single trait separate from each other. Alleles for a trait “recombine” at fertilization, producing the genotype for the trait of the offspring”

Law of Independent assortment

• Alleles for different traits are distributed to sex cells (& offspring) independently of one another. 

• Occurs when chromosomes line up during metaphase I and metaphase II

• Demonstrated in dihybrid crosses

How do we Organize Our Traits?

As per Law of Independent Assortment each pair of alleles segregates independently during gamete formation.

Formula: 2ⁿ (n = # of heterozygotes)

What gamete are produced from RrYy?

2² = 4 gametes

RY Ry rY ry

9:3:3:1

Phenotypic ratio for dihybrid crosses