unit 8 introduction to genetics chapter 8 (pg 144 – 147) chapter 9 (pg 164 - 183)
TRANSCRIPT
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