Unit 8Introduction to

Genetics

Chapter 8 (pg 144 – 147)Chapter 9 (pg 164 - 183)

Unit 8Lecture 1

Topics:DNA, Genes, Chromosomes, Karyotypes

Covers:Chapter 8-1 (pgs 144 – 147)

Genetics: Introduction

What is genetics? Genetics is the study of heredity, the process in

which parents pass on genes onto their children.

 

What does that mean?Children inherit their biological parents’ genes that

determine the child’s specific traits, such as physical features, gender, and genetic disorders.

DNA & GenesHeredity describes how traits are passed from parents

to their children.

Children inherit their genes from their mom and dad.Did you know…Humans have over 30,000 genes!

Genes determine some of your traits. Genes are small sections of DNA that code for a

specific protein.Genes are kept safe by being stored in molecules of

DNA.DNA is protected inside the cell by a structure known

as a nucleus.

DNA & Chromosomes

During normal cellular activity, DNA's info is copied into RNA, RNA is then sent to a ribosome to make the protein

During cell division, DNA is coils around histone proteins and condenses into a structure called a CHROMOSOMEWhen DNA is in chromosome form, it is visible under a

light microscope (DNA double helix not visible using a LM)

Diploid organisms have two sets of chromosomes. This means that each cell has two versions (a pair) of

each chromosomeCalled HOMOLOGOUS CHROMOSOMES –

chromosomes that are the same size, same shape and carry the genes for the same traits (one from each parent)

EVERY cell has DNA (chromosomes).Haploid (1n) – Cell with one set of chromosomes

Examples: Reproductive cells or asexually reproducing organismsHuman Haploid Cells = 23 chromosomes

Diploid (2n) – Cell with two sets of chromosomesExamples:

Body Cells (Somatic Cells)Human Diploid Cells = 46 chromosomes

(2 sets of 23 chromosomes)

Within each cell, there are two types of Chromosomes:Remember: Chromosomes/DNA store genes

1. SEX CHROMOSOME Sex Chromosomes are referred to as “X” or “Y”

(based on their shape)Female - XX  Male – XY

Chromosome that has the genes that determine the gender of the organism

Also has genes for other characteristicsKnown as SEX-LINKED GENES “Linked Genes” are genes that are found

on the same chromosome

2.  AUTOSOMEAll other chromosomes, don’t have gender genesCarries genes for many characteristicsAutosomes are numbered (biggest to smallest)

Humans - 46 chromosomes 2 sex chromosomes (1 pair - XX or XY)44 autosomes (22 pairs)

KARYOTYPE – profile of a person’s chromosomes, arranges chromosomes from largest to smallest, pairs homologous chromosomes

End Lecture 1

Unit 8

Unit 8Lecture 2

Topics: Introduction to GeneticsGregor Mendel

Covers:Chapter 9-1 (pg 164 – 167)

WHAT IS GENETICS?

Important People in Genetics:Gregor Mendel (1822 – 1884)

“Father of Modern Genetics”Watson & Crick

Discovered Structure of DNAThomas Hunt Morgan

Studied fruit flies (Drosophila melanogaster)

Discovered sex chromosomesNamed sex chromosomes “X” and “Y”

WHAT IS GENETICS?

Important People in Genetics:Gregor Mendel (1822 – 1884)

“Father of Modern Genetics”Austrian monk Studied pea plants (Pisum sativum)Noticed that not all pea plants looked identical. He studied 7 different traits and realized each

trait had 2 different appearances (two different versions). Now we refer to a “trait” as a “gene”

Seven Traits Mendel Studied

Note: You do not have to copy this chart into your notes.

Mendel’s Experiments

Mendel started growing plants that were “pure strains”A pure strain is when the

offspring always inherits the same trait as the parents

Once he was sure the strain was pure, he cross-pollinated the two different strains

Mendel bred plants together that had only one visible difference/variationKnown as a MONOHYBRID

CROSS

Mendel’s Experiments

Called the original plants – Parent (P1 generation)Called the first generation’s offspring – First Filial (F1

generation)

He would then repeat the process to study the appearance of the second generationSecond Filial (F2 generation)

P generation F1 generation F2 generation F3 generation

Results of F1 Generations

Note: You do not have to copy this chart into your notes.

Results of F2 Generations

Note: You do not have to copy this chart into your notes.

Note: You do not have to copy this chart into your notes.

Results of F2 Generations

Mendel’s Experiments

Based on his observations, and consistent data, Mendel was able to create several “Laws” of genetics.

Mendel demonstrated that the inheritance of traits (genes) follows a patternWe can use this pattern to predict the genetic

combination (appearance) of future generations

Although some of the terminology has changed and there are some exceptions to his Laws, Mendel is credited with the discovery of genetics

End of Lecture 2

Unit 8Lecture 3

Topics:Basic Laws of InheritanceMendelian Genetics

Covers:Chapter 9-1 (pg 164 – 169)

Basic rules of inheritance1. Genes exist in pairs

Remember: Homologous Chromosomes

2. There are different versions of each geneAllele – different versions of a gene; codes for a

different protein; produces different appearances

3. Usually, one allele is dominant Dominant alleles represented by a CAPITAL letter

Dominant allele masks the presence of the other allele

Recessive alleles represented by a lower case letterRecessive allele is the allele that is masked (covered

up)

Basic rules of inheritance

Because genes exist in pairs (homologous chromosomes), so do alleles. So when an organism's alleles are identified, it is in a pair (TT or tt)This combination of alleles is known as the organism's

GENOTYPEGENOTYPE - genetic makeup of an organism, allele

combination for a particular gene, determines phenotype

A PHENOTYPE is the observable trait resulting from a person’s allele combination for a gene.

Basic rules of inheritanceTypes of Genotypes

Homozygous – also known as “pure strain”Two of the same type of alleleTT – Homozygous Dominanttt – Homozygous recessive

Heterozygous – also known as “hybrid”Two different allelesTt

Basic rules of inheritance

4. LAW OF SEGREGATION

During formation of GAMETES (haploid cells, 23 chromosomes, sperm/egg), homologous chromosomes are separated and are placed into different cellsHappens during Meiosis I

Because the chromosomes are separated, this means that the alleles are separated.1 homologue (& its genes/alleles) goes to one gameteOther homologue (& its genes/allele) goes to the other

gamete

5. LAW OF INDEPENDENT ASSORTMENTHow one pair of homologous chromosomes is separated

does not affect how the other pairs are separated. The homologous chromosomes are sorted (separated):

Randomly & Independent of the other homologous pairs

i.e. Genes for different traits are inherited independently of each other

Example: 2 different pairs of homologous chromosomes: 1 pair has the gene for flower color, 1 pair has the

gene for Seed color. Pp = Flower Color  Yy = Seed ColorHow many combinations can be made?

1 "P" and 1 "Y”

Basic rules of inheritance

End of Lecture 3

Unit 8Lecture 4

Topics:Punnett Squares

Covers:Chapter 9-2 (pg 170 – 178)

Punnett Squares

Punnett Squares are used to predict the possible allele combinations between two parents (or gametes)

In a Punnett square:Each parents' alleles are represented Every possible combination of alleles

from the two parents are placed in the inside squares

Monohybrid CrossYou use a Punnett Square to predict the possible allele

combinations a child can inherit.To fill in a Punnett Square, you put one parent’s alleles

in the top column and the other parent’s alleles on the side rows.

MONOHYBRID CROSS – Cross between two organisms that have ONE difference/variationPredicting the possible combination of

alleles from one gene1 gene, 2 alleles1 homologous pair, 2 chromosomes

Dihybrid Cross

DIHYBRID CROSS – Cross between two organisms that have TWO differences/variationsUsed to predict the likelihood that two traits will be

inherited together (Ex: Brown hair and blue eyes)More complicated than a monohybrid cross because

there are more possible combinations

MONOHYBRID CROSS – 1 gene, 2 alleles1 homologous pair, 2 chromosomes

 DIHYBRID CROSS - 2 genes, 4 alleles2 homologous pairs, 4 chromosomes

Some Helpful Hints… In a cross between

Homozygous Dominant and Homozygous RecessiveResults – Offspring’s genotype is always Heterozygous

Homozygous and HeterozygousResults: (1:1 ratio)

50% chance offspring will be Homozygous (like parent)

50% chance offspring will be HeterozygousHeterozygous and Heterozygous

Results: (1:2:1 ratio)25% chance offspring will be Homozygous Dominant50% chance offspring will be Heterozygous25% chance offspring will be Homozygous recessive

End of Lecture 4