HEREDITY UNIT

Mendelian Genetics

Allele= Specific variation of a gene, often represented by using letters (ex. A, a)

Dominant Allele- Always shows in a phenotype if inherited (A)

Recessive Allele- Only shows in the phenotype if the dominant allele has not been inherited (a)

Genotype: the combination of inherited alleles, typically represented by two letters.

Homozygous- containing two of the same alleles (AA, aa)

Heterozygous-containing two different alleles (Aa)

Mendels laws describe the inheritance of genes and traits on different chromosomes.

Law of Segregation

-Chromosomes carry alleles. Homologous chromosomes carry alleles for the same trait. When chromosomes are separated into daughter cells during meiosis, the alleles for each trait are also separated. This separation of allleles allows for genetic variation among the gametes.

Each individual has two copies of each gene, and alleles are alternative versions of a gene. In homozygous, the alleles are identical, and in heterozygotes, the alleles are different. When individuals create gametes which are sex cells, they pass on only one of their two alleles.

Law of Independent Assortment

-Two or more genes assort independently of each other. One trait is not automatically inherited with another trait. Alleles for separate traits can be packaged in every possible combination for gametes.

Rules of probability can be applied to analyze passage of single gene traits from parent to offspring.

Determine probability of A or B= Add

Determine the probability of A + B= Multiply

Monohybrid Cross= Examination of how one trait is inherited

Dihybrid cross= Examination of how two traits are inherited.

Punnett squares are used to illustrate the probable outcomes of a cross.

Patterns of inheritance can often be predicted from data, including pedigrees.

-Visual representation tracing the history of a trait through familial generations.

-Helps to identify types of inheritance

-Circles represent biological females and squares represent biological males.

-Shaded= Affected Unshaded= Unaffected

-Generations= Roman numerals

Autosomal dominant traits= pattern of affected offspring with affected parents

Autosomal recessive traits= Pattern of affected offspring with unaffected parents

CHI SQUARE HYPOTHESIS TESTING

Hypothesis testing= Used by scientists to reject or fail statistical hypotheses, helps us determine if differences in numerical data are due to independent variable or due to chance.

Types of hypotheses= Null and Alternate

Chi-Square goodness of fit test

-Used to determine if there is a significant relationship between two groups of data

Observed outcomes are compared with expected outcomes

-OFTEN USED TO TEST GENETIC CROSSES, CAN ALSO BE USED FOR OTHER ANALYSES.

HOW TO

  1. Establish research question

  2. Determine null

  3. Determine Alt

  4. Count observed values

  5. Determine expected values

  6. Calculate chi-square value

  7. Calculate degrees of freedom

  8. Select P-value

  9. Identify critical value

  10. Compare chi-square value with critical value to draw conclusions

NON MENDELIAN GENETICS

Patterns of inheritance of many traits DO NOT follow the ratios predicted by Mendels Laws.

  • Genes that are adjacent and close to one another on the same chromosome and that are inherited together are known as linked genes.

  • Traits that are determined by genes located on sex chromosomes (X and Y) are known as sex-linked traits.

  • Linked genes and sex-linked traits DO NOT follow predicted ratios and can be identified by quantitative analysis.

Genes that are adjacent and close may appear to be genetically linked.

Linked Genes

  • Typically inherited together

  • Less likely to be seperated during crossing over in mitosis

The probabiliity that genetically linked genes will segregate as a unit can be used to calculate the map distance between them.

Map units can be used to determine the distance between genes on a chromosome.

Some traits are determined by genes on a sex chromosomes and they are known as sex-linked traits.

  • Located on sex chromosomes

  • Nonhomologous

  • Can have different letter designations (X/Y, Z/W)

The pattern of inheritance of sex-linked traits can often be predicted from data, including pedigree.

In humans:

  • Biological females contain two X chromosomes (XX), they can be carriers

  • Biological males contain an X and a Y chromosome (XY) they only have one x chromosome

  • The Y chromosome contains very little genetic info, therefore most sex-linked alleles are carried on the X chromosome.

Many traits are the product of multiple genes and/or physiological processes happening in combination

These traits DO NOT segregate in Mendelian patterns

Ex. Human Hair Colour- Determined by multiple genes.

A dominant allele codes for DARK pigment and a recessive allele DOES NOT

AABBCC= Darkest Hair Colour

aabbcc=Lightest Hair Colour

Some traits result from non-nuclear inheritance

  • Chloroplasts and mitochondria contain their own non-nuclear genome

  • Chloroplast and mitochondria are randomly assorted to gametes and daughter cells during cell division.

  • Mitochondria are transmitted to the egg and not sperm in animals; such traits are MATERNALLY INHERITED

  • Mitochondria and chloroplast are transmitted in the ovule and not in the pollen in plants; such are MATERNALLY INHERITED

  • Traits determed by chloroplast and mitrochondrial DNA cannot be predicted by Mendelian genetics.

Inheritance determined by multiple genes= larger number of possible genotypes

Non-nuclear inheritance- found in chloroplasrs + mitochondria; passed down maternally

Same genotype= multiple different phenotypes

Phenotypic plasticity= ability of one genotype to produce more than one phenotype

Phenotypic diversity=can be due to environmental factors.

THINGS IDK

Independent assortment- They separate independently of eahc other during gamete formation.

Law of segregation- two alleles for a traits separate during gamete formation, so that offspring recieve one from each paretn

Testcross- Used to determine unknown genotype by crossing it against a homozygous recessive individual

Polygenic traits- Single phenotypic trait is controlled by additive effects of mant genes, contributing each a small amount to the overall phenotype

Pleiotropy- Kinda opposite polygenic; a single gene has multiple phenotypic effects. can control many traits- Ex. Sickle cell amenia where theres amenia, heart

Epistasis-a gene at one locus alters phenotypic expressing of a gene at the second locys (one gene masks another)

Mitochondrial inheritance- the extranuclear genes are inhreited matterrnally because the cytoplasm comes from the egg. Defects in mitoochondrial genes prevent cells frmo making enough ATP and result in dideases affecting the muscular and nervous systems.

Genomic imprinting- in few mammalian traits, the phenotype depends on which parent passed along the alles (one allele silenced)

Aneuploidy- Results from fertilization of gamets in which nondisjunction occured

Nondisjunction- Pairs of homologous chromosomes do not separate normally during meiosis and one receives two which other recieves non.