Chapter 10: Sexual Reproduction and Genetics
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Chapter 10: Sexual Reproduction and Genetics. Fall 2011 Wood. Chapter Overview (p.268). Big Idea Reproductive cells, which pass on genetic traits from the parents to the child, are produced by the pattern of meiosis. Sections 1) Meiosis 2) Mendellian genetics

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Chapter overview p 268
Chapter Overview (p.268)

  • Big Idea

    • Reproductive cells, which pass on genetic traits from the parents to the child, are produced by the pattern of meiosis.

  • Sections

    • 1) Meiosis

    • 2) Mendellian genetics

    • 3)Gene linkage and polyploidy


Section 1 meiosis
Section 1: Meiosis

  • Each cell in the body has a specific number of chromosomes.

  • For humans, our cells contain 46 chromosomes.

  • We receive 23 chromosomes from the mother, and 23 chromosomes from the father


Human cells
Human Cells

  • Where do our 46 chromosomes come from?

  • Having 2 sets of DNA is called having homologous chromosomes.

    • Same chromosome but carrying different versions of traits.



Haploid cells
Haploid Cells

  • A cell that contains one set of chomosomes (n) is considered haploid (half-loid).

    • For humans these cells would only have 23 chromosomes

    • These cells are called gametes


Diploid cells
Diploid Cells

  • These are cells that contain 2 sets (2n) of chromosomes.

    • For humans, these would be normal cells with 46 chromosomes



Gamete formation
Gamete formation

  • Gametes, or haploid cells, are formed during a process called meiosis.

  • Meiosis starts with one diploid cell, and ends up creating 4 haploid cells.

  • Meiosis is split into 2 divisions:

    • Meiosis I

    • Meiosis 2


Interphase
Interphase

  • These cells still must go through interphase prior to meiosis.

  • This allows the cell to make a copy if the DNA during the S-Phase


Meiosis i
Meiosis I

  • First phase is Prophase I

    • Chromosomes condense

    • Nuclear membrane dissolves


Metaphase i
Metaphase I

  • Homologous chromosomes align on the equator.


Anaphase i
Anaphase I

  • Homologous chromosomes separate and move to opposite poles.


Telophase i
Telophase I

  • Chromosomes uncoil to form 2 nuclei

  • The cell divides.


Meiosis ii
Meiosis II

  • Prophase II

    • Repeat of prophase 1


Metaphase ii
Metaphase II

  • Haploid number of chromosomes align on the midline.


Anaphase ii
Anaphase II

  • Sister chromatids are pulled to opposite poles.


Telophase ii
Telophase II

  • Chromosomes reach the poles, and nuclear membranes form.


Cytokinesis ii
Cytokinesis II

  • Meiosis results in 4 haploid cells each with n number of chromosomes.


Importance of meiosis
Importance of Meiosis

  • Creates 4 haploid daughter cells that are not identical.

  • Results in genetic variation

    • Random creation of gametes

    • Ex) crossing over


Crossing over
Crossing over

  • Occurs during prophase I to create genetic variation.

  • Happens when parts of chromosomes are traded between a pair of homologous chromosomes.


Section 2 mendellian genetics
Section 2: Mendellian genetics

  • Overview

    • Start of genetics

    • Alleles

    • Dominant and recessive

    • Genotype and phenotype

    • 2 laws of genetics

    • Punnett squares


The start of genetics
The start of genetics

  • In 1866, Greger Mendel published his findings on inheritance.

  • He is now known as the “Father of Genetics”

  • He was an Austrian monk who studied garden pea plants.



Generations
Generations

  • The parent generation is also known as the “P” generation.




Alleles
Alleles there not green?

  • The alleles for our example are yellow and green.

  • An allele is simply an alternate form of a gene.

  • One allele will be dominant and the other will be recessive.



Dominant vs recessive
Dominant They were not there in the second generation. vs Recessive

  • Dominant alleles are always shown by a capital letter. Recessive genes are always shown by a lowercase letter.

    • Ex) yyYYYy

      • Green yellow yellow


Homozygous vs heterozygous
Homozygous They were not there in the second generation. vs heterozygous

  • An individual can be one of 3 types:

    • Homozygous dominant

    • Heterozygous

    • Homozygous recessive


Genotype vs phenotype
Genotype They were not there in the second generation. vs Phenotype

  • A genotype is what genes an individual has.

  • A phenotype is what characteristics are observed.

  • Yyvsyyvs YY


Law of segregation
Law of Segregation They were not there in the second generation.

  • States that two alleles for a gene must separate during meiosis.


Law of independent assortment
Law of Independent Assortment They were not there in the second generation.

  • This law states that alleles occur in a random distribution.

    • Aka) the genes from one parent do not always stay together.


2 laws of genetics
2 Laws of Genetics They were not there in the second generation.

  • Mendel formulated 2 laws for genetics:

    • 1) Law of Segregation

    • 2) Law of Independent Assortment


Punnett squares
Punnett They were not there in the second generation. Squares

  • These predict the possible offspring of a cross between two known genotypes.

  • Monohybrid cross


Section 3 gene linkage and polyploidy
Section 3: Gene Linkage They were not there in the second generation. and Polyploidy

  • Overview

  • Genetic recombination

  • Gene Linkage

  • Polyploidy


Genetic recombination
Genetic Recombination They were not there in the second generation.

  • The new combination of genes produced by crossing over and independent assortment is called genetic recombination.

  • Human cells have a possible 223 combinations. Combine 2 cells and there are over 70 trillion possibilities.


Gene linkage
Gene Linkage They were not there in the second generation.

  • Genes that are located close to one another on a chromosome are said to be linked. This means that they usually travel together during meiosis.


Polyploidy
Polyploidy They were not there in the second generation.

  • This is the occurance of one of more extra sets of chromosomes in an organism.

  • Ex) strawberries are 8n, coffee is 4n, and wheat is typically 6n.


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