BIOL 1406 Lecture 12: Biology notes ch. 13

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8 Feb 2017
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Chapter 13: Meiosis and Sexual Reproduction
Comparison of Asexual and Sexual Reproduction
In asexual reproduction, one parent produces genetically identical offspring
A clone
This is done by Mitosis
Cellular division
Sexual reproduction
In sexual reproduction, two parents give rise to offspring that have unique combinations of
genes inherited from the two parents
Variation is the result
Why is sexual reproduction so common?
What are the pros and cons of sexual and asexual reproduction?
Speed?
Energy demands?
Safety?
Why does nearly every organism reproduce sexually?
Genetics
Variation is produced by the process of sexual reproduction
Why is variation important?
Genetics
the scientific study of heredity and variation
Heredity is the transmission of traits from one generation to the next
Inheritance of Genes in Sexual Reproduction
Genes are the units of heredity, and are made of DNA
Each gene has a specific location called a locus on a certain chromosome
Genes are passed from parent to offspring through reproductive cells called gametes (sperm and
eggs)
One set of chromosomes are inherited from each parent
Sets of Chromosomes in Human Cells
The two chromosomes in each pair are called homologous chromosomes
Human somatic (body) cells have 23 pairs of chromosomes
Homologous pairs carry genes controlling the same inherited characters
Thus we all carry two genes for each trait
The 23rd chromosome pair are called the sex chromosomes
Human females have a homologous pair of X chromosomes (XX)
Human males have one X and one Y chromosome (XY)
The 22 pairs of chromosomes that do not determine sex are called autosomes
Concept 13.3: Meiosis reduces the number of chromosome sets from diploid to haploid
Meiosis is preceded by the replication of chromosomes
Meiosis takes place in two sets of cell divisions
meiosis I and meiosis II
The two cell divisions result in four haploid cells
Each daughter cell has only half as many chromosomes as the parent cell
Sexual reproduction is made possible by the process of meiosis
Gametes (egg and sperm) are created
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