Biology Semester 2 Freshman Year - Unit 10: Genetics

somatic cells

body cells

somatic cells = diploid or haploid

diploid (2n = 2 sets of chromosomes)

gametes

sex cells

gametes = diploid or haploid

haploid (n = 1 set of chromosomes)

2 types of chromosomes that our bodies contain

Autosomes and Sex Chromosomes

Autosomes

Chromosomes that carry traits that make you who you are

• Ex: 1^st 22 pairs of chromosomes

Sex Chromosomes

chromosomes that carry traits that make who you are and determine your biological sex (male or female)

• Ex: the 23rd pair of human chromosomes (X or Y)

meiosis

process of cell division that makes gametes

meiosis results in production of….

four haploid sex cells / gametes (egg = female or sperm = male)

fertilization

actual fusion of egg and sperm to form a zygote

homologous chromosomes

chromosome pairs that have the same types of genes

• (one from mom, one from dad)

sister chromatids

identical copies of the same chromosome

purpose of meiosis

make gametes HALF the normal number of chromosomes (only 1 set)

meiosis make gametes/sex cells that have half the normal number of chromosomes (only 1 set rather than 2). How?

cell division happens twice in Meiosis

Meiosis I results in…

separation of homologous chromosomes

Meiosis II results in…

separation of sister chromatids

• Duplicated chromosomes from Meiosis I divide into individual chromosomes.

DNA replicates during…

S phase (interphase)

Prophase in Meiosis 1

Each replicated chromosome pairs with its homologous chromosome, and crossover happens

crossover

swapping of DNA between the homologous chromosome pairs

crossover happens during..

prophase 1 of meiosis

is there any DNA replication prior to meiosis 2?

no

in meiosis 2, …

sister chromatids are pulled apart

Nondisjunction

Failure of chromosomes to separate in meiosis; leads to aneuploidy (extra or missing chromosomes)

gene

section of DNA that provides the instructions for making a protein

Alleles

different versions of the same gene

Gregor Mendel

Austrian monk who used pea plants to learn about genetics. He is known as the “father of genetics”.

Three laws of inheirtance

Law of Dominance, Law of Segregation, Law of Independent Assortment

Law of Dominance

Dominant trait always expresses itself over the recessive

Law of Segregation

When chromosomes separate in meiosis, each gamete will receive only one chromosome from each pair.

Law of Independent Assortment

the assortment of chromosomes for one trait doesn’t affect the assortment of chromosomes for another trait

Punnet Square

a diagram that shows the probability of inheriting traits from parents with certain genes

Monohybrid cross

a cross between two organisms looking at one trait

Dihybrid crosses

Used when finding the possible genotypes for offspring when considering two traits at the same time

Probability

Can be used to determine the outcome of genetic crosses

Incomplete Dominance

neither allele is completely dominant or recessive

• example = red + white flowers make pink flowers

Co-dominance

both traits are expressed; Ex. red + white flower = red & white flower

Multiple Alleles

Having more than 2 alleles for one gene

Blood type inheritance pattern

Co-dominance and multiple alleles

Polygenic Inheritance

a trait produced by two or more genes

Epistasis

when one gene overshadow all of the others

• ex. Labrador retriever fur colors, eye color, Albinism 

linked genes

genes that are physically located on the same chromosome and will be inherited together

the only time linked genes can be separated or broken apart is during…

crossover

Sex-linked genes

genes on the sex chromosomes

carrier

someone who carries the recessive trait but isn’t affected by it

X-linked genes

• females inherit X-linked genes as normal and the principle of dominance applies

• Males inherit the gene on the X but not the Y so they will be affected if they get the recessive gene

Barr Bodies

Inactive X-chromosome in females

Aneuploidy

when an organism has missing or extra chromosomes

monosomy

missing chromosome from a pair

Trisomy

three copies of a chromosome instead of two

Karyotype

Visual representation of the number, size and structure of a person’s chromosomes

pedigree

chart used to trace the phenotypes and genotypes in a family to determine whether people carry diseases or traits

square in a pedigree represents a….

male

circle in a pedigree represents a…

female

Autosomal recessive trait

common inheritance pattern, the disease is rare in the family, disease skips generations, and males & females are equally likely to inherit the disease

Autosomal dominant trait

disease is common in the family, it never skips generations and males & females are equally likely to inherit this disease

Sex-linked recessive trait

the disease is rare in the family, more males are affected, the disease often skips generations, and affected fathers don’t pass on their trait to their sons

Affected fathers in a sex linked trait cannot pass their trait to their son. Why?

they only contribute the Y chromosome to the males and only pass on their X trait to the females

First step to find the pattern of inheritance in a pedigree

If there are way more males than females affected (shaded in) then the pedigree is tracing a Sex-Linked trait.

If not, look for two parents that are the same shade that have a child who is different from them.  Label that child homozygous recessive (Ex. rr) and the parents heterozygous (Ex. Rr) 

second step to determine the pattern of inheritance in a pedigree if you determine it not to be a sex linked trait

Look for two parents that are the same shade that have a child who is different from them.  Label that child homozygous recessive (Ex. rr) and the parents heterozygous (Ex. Rr) 

• If the child was shaded, the pedigree is tracing an Autosomal Recessive trait. 

• If the parents were shaded, the pedigree is tracing an Autosomal Dominant trait. 

phenotype

the physical traits of an organism; Ex. Purple flowers

genotype

actual alleles inherited; Ex. AA, Aa, aa