Mendelian Genetics Unit 3 Notes What is genetics
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Mendelian Genetics Unit 3 Notes
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 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 • 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 • 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 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 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 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 • 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 • 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 assortment
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
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 known genotypes
Practice!!!
Dominance and Multiple Alleles
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
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) • ABO blood groups have three forms of alleles
Practice!
Sex-Linked Traits
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 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 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 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 • 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 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 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 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
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 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 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
- Family resemblance test
- Dominant
- Section 11-5 linkage and gene maps answer key
- Carrier female genotype
- Chapter 7 extending mendelian genetics study guide answers
- Section 11-3 exploring mendelian genetics
- Chapter 10 section 2 mendelian genetics answer key
- Mendelian genetics punnett square
- 11-3 exploring mendelian genetics
- 11-3 exploring mendelian genetics
- Holandric genes
- Extension of mendelian genetics
- Section 11-3 exploring mendelian genetics answer key
- Hors xnxn
- Extending mendelian genetics
- Pleiotropism definition
- Codominance example
- Mendel's experimental design
- Mendelian genetics
- What are mendelian traits
- Mendelian genetics vocab
- Non mendelian genetics codominance
- Color blind male and normal female
- Mendelian genetics concept map
- Chapter 7 extending mendelian genetics vocabulary practice
- Exploring mendelian genetics
- Blood type matrix
- Non mendelian inheritance
- Mendelian randomisation
- Non mendelian law
- Non mendelian law
- Cystic fibrosis mendelian inheritance
- Mendelian traits
- Postulat mendel
- Probability laws govern mendelian inheritance
- Mendelian pattern of inheritance
- Difference between mendelian and chromosomal disorders
- Complete the punnett square
- Mendelian principles
- Recessive epistasis definition
- What is a dihybrid cross
- Mendelian traits
- Mendel
- Mendelian