Mendelian Genetics Unit 3 Notes What is genetics

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Mendelian Genetics Unit 3 Notes

Mendelian Genetics Unit 3 Notes

What is genetics? • The passing of traits to the next generation is called

What is genetics? • The passing of traits to the next generation is called inheritance, or heredity

Gregor Mendel • Gregor Mendel performed crosspollination in pea plants • Mendel followed various

Gregor Mendel • Gregor Mendel performed crosspollination in pea plants • Mendel followed various traits in the pea plants he bred • He is known as the “father of genetics”

Mendelian Genetics • The parent generation is also known as the P generation •

Mendelian Genetics • The parent generation is also known as the P generation • The offspring of this P cross are called the first filial (F 1) generation • The second filial (F 2) generation is the offspring from the F 1 cross

Mendel’s Studies • Mendel studied seven different traits: • Seed or pea color •

Mendel’s Studies • Mendel studied seven different traits: • Seed or pea color • Flower color • Seed pod color • Seed shape or texture • Seed pod shape • Stem length • Flower position

Genes in Pairs • Allele • An alternative form of a single gene passed

Genes in Pairs • Allele • An alternative form of a single gene passed from generation to generation • Dominant • One alleles masks the other • Recessive • The allele that is masked

Dominance • An organism with two of the same alleles for a particular trait

Dominance • An organism with two of the same alleles for a particular trait is homozygous • An organism with two different alleles for a particular trait is heterozygous

Genotype and Phenotype • An organism’s allele pairs are called its genotype • The

Genotype and Phenotype • An organism’s allele pairs are called its genotype • The observable characteristic or outward expression of an allele pair is called the phenotype

Mendel’s Law of Segregation • Two alleles for each trait separate during meiosis •

Mendel’s Law of Segregation • Two alleles for each trait separate during meiosis • During fertilization, two alleles for that trait unite • Heterozygous organisms are called hybrids

Law of Independent Assortment • Random distribution of alleles occurs during gamete formation •

Law of Independent Assortment • Random distribution of alleles occurs during gamete formation • Genes on separate chromosomes sort independently during meiosis • Each allele combination is equally likely to occur

Genetic Recombination • The new combination of genes produced by crossing over and independent

Genetic Recombination • The new combination of genes produced by crossing over and independent assortment

Twin Studies • Helps scientists separate genetic contributions from environmental contributions • Traits that

Twin Studies • Helps scientists separate genetic contributions from environmental contributions • Traits that appear frequently in identical twins are at least partially controlled by heredity • Traits expressed differently in identical twins are strongly influenced by environment

Punnett Squares

Punnett Squares

Monohybrid Cross • A cross that involves hybrids for a single trait is called

Monohybrid Cross • A cross that involves hybrids for a single trait is called a monohybrid cross

Punnett Squares • Used to predict the possible offspring of a cross between two

Punnett Squares • Used to predict the possible offspring of a cross between two known genotypes

Practice!!!

Practice!!!

Dominance and Multiple Alleles

Dominance and Multiple Alleles

Incomplete Dominance • The heterozygous phenotype is an intermediate phenotype between the two homozygous

Incomplete Dominance • The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes. • It is a mix of physical appearance between the dominant alleles • Dominant alleles represented by a capital letter in crosses • Example: R or W

Other ways of writing Incomplete Dominance

Other ways of writing Incomplete Dominance

Codominance • When an individual is heterozygous for such traits, both alleles for one

Codominance • When an individual is heterozygous for such traits, both alleles for one trait in an individual are expressed equally • In other words, 2 types of alleles that are equally dominant • Phenotype of the heterozygote has both traits simultaneously • Both alleles are dominant, so they are both represented by a capital letter: B, W or CB, CW (superscript)

Multiple Alleles • Blood groups in humans (this shows both multiple alleles and codominance)

Multiple Alleles • Blood groups in humans (this shows both multiple alleles and codominance) • ABO blood groups have three forms of alleles

Practice!

Practice!

Sex-Linked Traits

Sex-Linked Traits

Karyotype Studies (not being tested on) • Karyotype—micrograph in which the pairs of homologous

Karyotype Studies (not being tested on) • Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size • Images of chromosomes stained during metaphase • Chromosomes are arranged in decreasing size to produce a micrograph

Telomeres (don’t need to write down) • Telomere caps consist of DNA associated with

Telomeres (don’t need to write down) • Telomere caps consist of DNA associated with proteins • Serves a protective function for the structure of the chromosome • They might also be involved in aging and cancer

Nondisjunction (not being tested on) • Cell division during which sister chromatids fail to

Nondisjunction (not being tested on) • Cell division during which sister chromatids fail to separate properly • If this occurs during Meiosis I or II then the resulting gametes will not have the correct number of chromosomes • Down syndrome: nondisjunction occurred on chromosome 21. • The result is short stature, heart defects, and mental disability

Chromosome Inactivation • Barr bodies: the inactivated X chromosome in females • One X

Chromosome Inactivation • Barr bodies: the inactivated X chromosome in females • One X chromosome is randomly inactivated in an early embryonic cell • Example: Tortoise shell cats • The gene for coat color is on the X chromosome. • When the cat is heterozygous in coat color (black/orange) it is born with patches of different colored fur on its body.

Sex-Linked Traits • Traits are controlled by genes located on the sex chromosomes •

Sex-Linked Traits • Traits are controlled by genes located on the sex chromosomes • Humans: 22 homologous pairs of matching chromosomes called autosomes, and one pair of sex chromosomes (XX or XY) • There are genes found on the X chromosome that are not found on the Y chromosome • Inheritance of traits determined by these genes is therefore linked to the sex of the individual

X-linked Traits • Genes located on the X chromosome that control traits • Since

X-linked Traits • Genes located on the X chromosome that control traits • Since males have only 1 X chromosome they are affected by recessive X-linked traits • Females are less likely to express a recessive trait because she has two X chromosomes. One of the X chromosomes can mask the affect of the trait.

Sex Determination • Sex chromosomes determine an individual’s gender • Autosomes are all the

Sex Determination • Sex chromosomes determine an individual’s gender • Autosomes are all the other chromosomes that determine everything else. (i. e. Body cells) • The Y chromosome determines the sex of the organism • XX=Female; XY=Male

When completing crosses… • When writing genotypes: • Put the trait gene as a

When completing crosses… • When writing genotypes: • Put the trait gene as a superscript to the sex chromosome • XR XR ; X R Y • Capital letter represents a dominant allele and lowercase letter represents a recessive allele

Examples (to name a few) • Red-Green Color Blindness • Hemophilia

Examples (to name a few) • Red-Green Color Blindness • Hemophilia

Ex: Hemophilia • Recessive sex-linked disorder characterized by delayed clotting of the blood. •

Ex: Hemophilia • Recessive sex-linked disorder characterized by delayed clotting of the blood. • Very rare in females because she would need to have both X chromosomes with the recessive trait.

Types of Genotypes • XHXH (female with normal blood clotting) • XHXh (female with

Types of Genotypes • XHXH (female with normal blood clotting) • XHXh (female with normal blood clotting, but is a carrier of the trait) • Xh. Xh (female with hemophilia) • XHY (male with normal blood clotting) • Xh. Y (male with hemophilia)

Ex: Red-Green Color Blindness • This is a recessive X-linked trait. A male only

Ex: Red-Green Color Blindness • This is a recessive X-linked trait. A male only needs one copy of this allele in order to be colorblind • A female would need to have two copies of the recessive allele. Thus it is very rare to find a color blind female