BIOL 103 Week 11 - Meiosis Inheritance

Define the term: meiosis

a type of reproduction a cell can go through

Mitosis vs. Meiosis

Mitosis creates identical copies while meiosis creates unique variations

Define the term: Diploid

a cell or organism that contains 2 copies of every chromosome, one from each parent

Define the term: Haploid

a cell or organism that contains a single set of unpaired chromosomes

Haploid gametes fuse to form…

diploid zygotes

Name the two types of cells and how they are made:

1. animal somatic cell = made by mitosis

2. animal reproductive (sex) cell = made by meiosis

Define the term: Locus (plural loci)

the location of a gene on a chromosome

Define the terms: Homozygous vs Heterozygous

1. Homozygous: inheriting identical alleles of a specific gene from BOTH parents (ex. AA or AA)

2. Heterozygous: inheriting different alleles of a gene (ex. Aa), where the dominant trait is usually expressed

Allele vs Gene

the allele is the variation part of the gene

Gives examples of dominant alleles vs recessive alleles

• no freckles vs freckles

• widows peak vs straight hairline

Define the term: Nondisjunction (and what happens with fertilization)

the failure of chromosomes or chromatids to separate during meiosis

• fertilization after nondisjunction yields zygotes with altered numbers of chromosomes

Define the term: Zygotes

a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum (ovum - a mature female reproductive cell)

What can you see with nondisjunction?

1. monosomy - Turner syndrome

2. trisomies (most common: trisomy 21 - down syndrome, trisomy 18 - Edwards syndrome, trisomy 13 - patau syndrome)

3. Other sex chromosome aneuploidy

Define the term: homologous recombination

a genetic process where two similar or identical DNA molecules exchange nucleotide sequences

Define the term: independent assortment (where does it occur - mitosis or meiosis?)

describes how pairs of alleles for different traits separate independently of one another during the formation of reproductive cells (gametes) (occurs in meiosis)

Random fertilization of eggs by sperm further…..

increases possibilities for variation in offspring (meiosis)

Define the terms: Genotype vs Phenotype

1. Genotype: an organism genetic makeup that is inherited

2. Phenotype: an organisms observable physical traits and behavior

What do phenotypes result from?

Results from genes and enviromental factors

What does tetrad formation lead to?

Recombination

Define the term: Crossing Over

the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring

Define the term: allele

a version of a gene

What does Crossing Over do?

it dosen’t create new copies, but it does make new combinations of alleles

Give two examples of this: Many genes have more than two alleles in the population. Not all traits are governed by a single gene with two alleles.

1. blood types (parent one has type A blood, parent two has type B blood, offspring can have type A blood, type AB blood, or Type B blood)

2. the mixing of a red rose and a white rose can produce a pink rose

Define the term: Pleiotrophy

One gene influencing many characteristics

The gene for sickle cell disease affects what?

• affects the type of hemoglobin produced

• affects the shape of red blood cells

• causes anemia

• causes organ dames

• is related to susceptibility to malaria

What are phenotypic variations influenced by?

by the enviroment

Give an example of polygenic inheritance

skin color is affected by at least three genes

Define the term: cystic fibrosis

a genetic disease caused by a single gene mutation

Can people with normal phenotypes still pass the Cystic Fibrosis allele to offspring?

YES

Will people with Cystic Fibrosis ALWAYS have offspring with CF

NO

How do chromosomes and genes contribute to traits?

Chromosomes are long strands of DNA that contain many genes. Each gene acts as an instruction manual for building specific proteins. These proteins then determine an organism's physical characteristics, or traits, such as eye color or height.

Humans have ___ chromosomes total

46

Human chromosomes exist as ___ pairs called _____ chromosomes

1. 23 pairs

2. homologous

Each human chromosomes pair containens one chromosome from ____ and one from ____

1. egg

2. sperm

What problem would occur if gametes were diploid instead of haploid?

The offspring would havee double the numberr of chromosomes after fertilization.

How does meiosis create genetic diversity?

Through crossing over and independent assortment

Gameates are ___ (n or 2n)

n

Somatic cells are ___ (n or 2n)

2n

If a cell has 23 chromosomes, is it haploid or diploid? Explain.

It is a haploid. Haploids have 23 chromosomes (one complete set) and diploid zygotes have 46 chromosomes (2 complete sets)

Name the differences between Mitosis and Meiosis:

1. number of divisions

2. number of cells produced

3. genetic similarity

4. cell type produced

Mitosis:

1. number of divisions: 1

2. number of cells produced: 2

3. genetic similarity: genetically identical

4. cell type produced: somatic

Meisosis:

1. number of divisions: 2

2. number of cells produced: 4 daughter cells

3. genetic similarity: genetically unique

4. cell type produced: gamates

Which process is used to “

1. make body cells?

2. make gametes?

1. mitosis

2. meiosis

In meiosis, DNA replication occurs ____ time(s)

1 time

In meiosis, Cell division occurs ____ time(s)

2 times

Why is meiosis NOT just “mitosis twice”?

Crossing Over and recombination creates genetically UNIQUE offspring. Mitosis creates genetically IDENTICAL cells. Also, in meiosis, cells divide twice but only replicates DNA once (a diploid cell to 4 haploid daughter cells)

Homologous chromosomes pair up in a structure called a ____

tetrad

What is tetrad formation called?

Synapsis

During cross over:

1. DNA is exchanged between _____ chromatids

2. This creates new combinations of _____

1. non-sister

2. alleles

Why is crossing over important for evolution?

because it increases genetic variation within a population. Ensures offspring are genetically unique

Meiosis II is most silimar to:

mitosis

What separates in Meiosis II?

the sister chromatids

The final results of Meiosis are: (cells, haploid/diploid. identical/unique)

• 4 daughter cells

• diploid

• unique

Crossing over creates_______

genetic recombination

Independent assortment » chromosomes line up ______ at metaphase I

randomly

Random fertilization: any ____ and fuse with any ____

1. sperm

2. egg

Why can humans produce millions of genetically different gamates?

Independent assortment (over 8 million possible combinations of chromosomes)

• when you add crossing over with independent assortment, you get infinite possibilities

Define the term: Gene

a specific sequence of DNA that codes for a functional product (ex. protien)

Define the term: allele

an alternative version of a gene

If genotype = Bb, is it homozygous or heterozygous?

Heterozygous

Define the terms: dominant vs recessive alleles

Dominant: expresses its phenotypes even when 1 copy is present (B)

Recessive: only expresses its phenotypes when 2 copies are present (b)

Why can a recessive trait “disappear” and the reappear later?

because the recessive trait was being masked by the dominant trait

Sex lined genes are located on the _____ chromosome

X

Sex-linked genes: males are more affected because…

they only have one X

Why are males more likely to express X-linked recessive disorders?

Male: XY » any recessive allele on the X chromosome will be expressed

Female: XX » the 2nd X chromosome maskes the affected gene

Nondisjunction occurs when…

chromosomes or chromatids fail to separate during meiosis

How does nondisjunction lead to Down syndrome?

Chromosome 21 fails to separate properly during meiosis

Define the term: incomplete dominance (give example)

heterozygous phenotype is a blend of 2 homozygous phenotypes

• red flower (RR) x white flower (rr) = pink flower (Rr)

Define the term: codominance (give example)

both alleles are fully expressed in the heterozygote

• AB blood type

Define the term: polygenic inheritance (give example)

the interaction of multiple genes

• skin color, height, etc.

Why don’t most human traits follow simple dominant/recessive patterns?

Because many traits polygenic. Environmental factors also influence how genes are expressed.