Genetics/inheritance

Trait

a genetically determined characteristic

Alleles

One, two or more versions of DNA sequences

Dominant trait

Dominant traits are always expressed, even if only one copy of the dominant trait exists

Recessive trait

Recessive traits are only expressed if both alleles are recessive, if one is dominant the recessive trait is masked

homozygous

two identical pairs of alleles of a particular gene

heterozygous

two different alleles of a particular gene

Genotype

genetic information

Phenotype

set of observable physical traits

Law of domincance

\-In a heterozygote, a dominant allele will mas the expression of a recessive allele

\-The only way to express a recessive allele is as a homozygote (absence of dominant allele)

Law of segregation

\-A diploid individual has 1 pair of alleles for each gene

\-When gametes are formed, this pair is randomly separated into 2 gametes.

\-Each gamete are haploid (contain 1 copy of each chromosome

\-which allele is passed to offspring is random

Law of independent assortment

\-the alleles of two (or more) different genes get sorted into gametes independently of one another

\-the allele a gamete receives for one gene does not influence the allele received for another gene

3 laws of inheritence

Law of independent assortment, Law of segregation, Law of domincance

Punnett square

a diagram used to predict genotypes of a cross

Incomplete dominance

a form of Gene interaction in which both alleles of a gene are partially expressed, often resulting in an intermediate or different phenotype

Representing alleles

exponents for the different dominant alleles

Example of co-dominance

ABO blood groups

Genes

The basic unit of heredity (made up of sequences of DNA) passed from parent to child.

Homologous chromosome

chromosomes that are present in the same chromosome pair

Sex chromosomes

two types of chromosomes, x and y, which determine the sex

Autosome (Chromosome)

the first 22 homologous pairs of human chromosomes that do not determine the sex of an individual

Co-dominance

a type of inheritence in which two alleles get expressed equally in the phenotype of a heterozygous individual

Incomplete dominance

when pairs of alleles are both expressed to form a new phenotype of a heterozygous individual

X-linked

a type of recessive inheritance which refers to genetic conditions associated with mutations in genes on the X chromosome (mostly in males)

Monohybrid cross

a mix between two sets of homozygous genotypes (completely dominant or completely recessive alleles) which result in opposite phenotypes for a certain genetic trait.

Pedigree

Shows a relationship between genetically related individuals, including the occurrence and appearance of phenotypes of a particular gene from one generation to the next

Pedigree rules (Females, Males, Shaded, Half-shaded, generation, numbering)

\-Females represented by circles

\-Males represented by squares

\-Shaded, means an individual is affected by the disease or disorder

\-Half-Shaded, means an individual is a carrier of the disease or disorder

\-Shows only phenotypes

\-Same generation on the same row

\-Roman numeral number generations

\-Arabic numerals number individuals in the same generation

Types of inheritence from pedigree charts

autosomal dominant, autosomal recessive, x linked dominant, x linked recessive

autosomal dominant

\-cannot be recessive as two affected parents cannot have an unaffected child

\-parents must be heterozygous

autosomal recessive

\-cannot be dominant as two unaffected parents cannot have an affected child

\-parents must be heterozygous

x linked dominant

\-affected daughters from an affected father suggest x linked dominance

\-sex linkage cannot be confirmed

x linked recessive

\-affected sons from affected mothers suggests x-linked recessive

\-sex linkage cannot be confirmed

To identify **sex-linkage** look for:

\-Usually only males affected

\-Rarely seen, but females affected only when the father is affected

To identify **autosomal recessive** look for:

\-Both males and females affected

\-Cases where two unaffected parents have an affected child

\-‘Skips’ generations

To identify **autosomal dominant** look for:

\-Every affected individual has at least one affected parent

\-Both males and females affected

\-Seen in every generation

Blood types

A, B, AB, O

A heterozygous

I^A i

A homozygous

I^A, I^A

B heterozygous

I^B, i

B homozygous

I^B, I^B

O

i, i