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Meiosis & Chromosomes

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by

Cana Rogers

on 18 February 2015

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Transcript of Meiosis & Chromosomes

MEIOSIS
You have 2 different types of cells in your body:
1. Somatic
2. Gametes
Homologous Chromosomes
One from father, one from mother
How are these chromosomes the same?
How are they different?
All chromosomes are called AUTOSOMES
With ONE exception!
Sex Chromosomes:
Determines whether you are male or female

- XX = ??
- XY = ??
Diploid Vs. Haploid
Diploid= two copies of each chromosome
Haploid= one copy of each chromosome
Meiosis
Divides the nucleus and DNA into haploid cells
How is Meiosis different than Mitosis?
2 Ways:
1. Reduces chromosome number
2. Creates genetic diversity
What's the difference between homologous chromosomes and sister chromatids?
MEISOSIS I:
division of homologous chromosomes
Prophase I:
nuclear membrane dissolves
centrioles move to opposite sides
spindle fibers assemble
homologous chromosomes pair up
Metaphase I:
homologous chromosomes pair randomly & line up in the MIDDLE
Crossing Over occurs
FACT: since humans have 23 pairs of chromosomes, Meiosis can result in 2 or 8,388,608 possible combinations
Anaphase I:
Paired homologous chromosomes separate from each other and move toward ends
sister chromatids stay together
Telophase I:
Nuclear membrane forms
spindle fibers disassemble
cytokinesis
Meiosis II:
divides sister chromatids
Prophase II:
nuclear membrane dissolves
centrioles move to opposite sides
spindle fibers assemble
Metaphase II:
spindle fibers align the 23 chromosomes at cell equator
sister chromatids are still together
Anaphase II:
Sister chromatids are pulled apart and move to ends
Telophase II:
Nuclear membrane forms
spindle fibers break apart
cytokinesis
Gregor Mendel
Australian Monk- 1800s
"the father of genetics"
Experiment
-PUREBRED organisms were the "P" generation
- F 1 cross resulted in F 2 of purple & white flowers with a ratio of 3:1
Studied 7 Traits in Pea Plants:
1. pea shape
2. pea color
3. pod shape
4. pod color
5. plant height
6. flower color
7. flower position
Chose Pea Plants because...

1. Reproduce Quickly
2. Could Control Pollination
3. Had qualities that were either/or
Conclusions:
Traits are discrete inheritable units
Organisms inherit 2 genes: one from each parent
Organisms donate only one copy of each gene in their gametes
- therefore genes must separate during gamete formation
LAW OF SEGREGATION
STUDIED PEA PLANTS AND GENETIC HEREDITY
CHALLENGED IDEA THAT OFFSPRING TRAITS WERE A BLEND OF PARENTS GENETICS
- example: If the parents were purple & white, the offspring would be pink

Mendel used experimental design and data from thousands of pea plants to disprove this theory
3 Key Choices that lead to success
in his Experiment:
1. USED PUREBRED PLANTS
2. CONTROLLED BREEDING
3. OBSERVED 7 KEY TRAITS
Traits, Genes
& Alleles
"locus"
-exact
of a gene
location
like an address for your house
23
If alleles match: homozygous
PP
pp
If alleles are different: heterozygous
OR
Pp
homozygous dominant
homozygous recessive
Somatic cells: body cells
Gametes: reproductive cells
Can you name some?
c
can you name them?
Each human somatic cell has 46 chromosmes:
- 23 pairs (1 from each parent)
- two chromosomes that have the same length and general appearance
These paired chromosomes are called homologous chromosomes

a piece of DNA that provides a set of instructions to make a certain protein
gene:
allele:
any form of a gene that may occur at a specific locus
there are two alleles for each gene
- one on each homologous chromosome
alleles are either:
dominant: always expressed if present
recessive: only expressed if no dominant allele is present
Dominant alleles are written by a capital letter
P = purple
Recessive alleles are written by a lower-case letter
p= white
remember: the dominant will be expressed
the two alleles for a gene is called a:
GENOTYPE
how it is expressed is a:
PHENOTYPE
If purple is dominant (P) and white is recessive (p)

- what are the possible genotypes for this flower?
- what is the phenotype?
Full transcript