Transcript what is genetics? - Nutley Public Schools

Unit 8
Introduction to Genetics
Chapter 8 (pg 144 – 147)
Chapter 9 (pg 164 - 183)
Unit 8
 Lecture 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 & 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
 Examples:
 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:
 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:
 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:
 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
inside squares
the
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
from one gene
 1 gene, 2 alleles
 1 homologous pair, 2 chromosomes
alleles
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…
 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
 50% chance offspring will be Heterozygous
 25% chance offspring will be Homozygous recessive
End of Lecture 4