Unit 8 Introduction to Genetics Chapter 8 (pg 144 – 147) Chapter 9 (pg 164 - 183)

Unit 8 Lecture 1 Topics: Covers: DNA, Genes, Chromosomes, Karyotypes 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 & Genes Heredity 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 CHROMOSOME When 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 chromosome Called 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 organisms Human Haploid Cells = 23 chromosomes Diploid (2n) – Cell with two sets of chromosomes 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 characteristics Known as SEX-LINKED GENES “Linked Genes” are genes that are found on the same chromosome

2.  AUTOSOME All other chromosomes, don’t have gender genes Carries genes for many characteristics Autosomes 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 8 Lecture 2 Topics: Covers: Introduction to Genetics Gregor 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 DNA Thomas Hunt Morgan Studied fruit flies (Drosophila melanogaster) Discovered sex chromosomes Named 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/variation Known 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 generation Second 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.

Results of F2 Generations Note: You do not have to copy this chart into your notes.

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 pattern We 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 8 Lecture 3 Topics: Covers: Basic Laws of Inheritance Mendelian Genetics Covers: Chapter 9-1 (pg 164 – 169)

Basic rules of inheritance 1. Genes exist in pairs Remember: Homologous Chromosomes 2. There are different versions of each gene Allele – 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 letter Recessive 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 GENOTYPE GENOTYPE - 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 inheritance Types of Genotypes Homozygous – also known as “pure strain” Two of the same type of allele TT – Homozygous Dominant tt – Homozygous recessive Heterozygous – also known as “hybrid” Two different alleles Tt

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 cells Happens during Meiosis I Because the chromosomes are separated, this means that the alleles are separated. 1 homologue (& its genes/alleles) goes to one gamete Other homologue (& its genes/allele) goes to the other gamete

Basic rules of inheritance 5. LAW OF INDEPENDENT ASSORTMENT How 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 Color How many combinations can be made? 1 "P" and 1 "Y”

End of Lecture 3

Unit 8 Lecture 4 Topics: Covers: Punnett Squares 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 Cross You 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/variation Predicting the possible combination of alleles from one gene 1 gene, 2 alleles 1 homologous pair, 2 chromosomes

Dihybrid Cross DIHYBRID CROSS – Cross between two organisms that have TWO differences/variations Used 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 alleles 1 homologous pair, 2 chromosomes  DIHYBRID CROSS - 2 genes, 4 alleles 2 homologous pairs, 4 chromosomes

Some Helpful Hints… Homozygous Dominant and Homozygous Recessive In a cross between Homozygous Dominant and Homozygous Recessive Results – Offspring’s genotype is always Heterozygous Homozygous and Heterozygous Results: (1:1 ratio) 50% chance offspring will be Homozygous (like parent) 50% chance offspring will be Heterozygous Heterozygous and Heterozygous Results: (1:2:1 ratio) 25% chance offspring will be Homozygous Dominant 25% chance offspring will be Homozygous recessive

End of Lecture 4