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Genetics

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Sara Caira

on 12 February 2016

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Transcript of Genetics

GENETICS
Trait:
a characteristic that an organism can pass onto its offspring through its genes
Heredity:
the passing of traits from parents to offspring
Genetics:
the scientific study of heredity
Purebred:
an organism that always produces offspring with the same form of a trait as the parent; and organism that is homozygous for a trait
Gene:
a segment of DNA on a chromosome that codes for a specific trait
Alleles:
the different forms of a gene
Dominant allele:
an allele whose trait always shows up in the organism when the allele is present
Recessive allele:
an allele that is masked when a dominant allele is present
Hybrid:
an organism that has two different alleles for a trait; an organism that is heterozygous for a trait
Self-pollinating:
they contain both male and female parts, allowing them to reproduce without pollen from another plant.
The Father of Genetics
priest from Central Europe
mathematics and science in 1851
Mendel's discoveries formed the foundation of the scientific study of heredity called genetics.
The Pea Experiments
Mendel noticed some pea plants had similar traits to their parents.
He cross pollinated the plants by using the pollen on the flowers.
F1 Generation
: Cross pollinated a purebred tall plant with a purebred short plant.
Result - All tall.
Probability & Genetics
Mendel was the first scientist to recognize that the principles of
probability
can be used to predict the results of genetic crosses
Key Terms
When you toss a coin more than once, the results of one toss do not affect the results of the next toss
The probability that a tossed coin will land on:
heads = 50%
tails = 50%
Punnett Squares
Geneticists use
Punnet squares
to show all the possible outcomes of a genetic cross and to determine the probability of a particular outcome
25%
25%
25%
25%
Alleles
Key Terms
Individual alleles control the inheritance of
traits
.
Some
allele
s are dominant while other alleles are recessive.
A trait controlled by a dominant alleles always show up if they are present.
A trait controlled by a
recessive allele
will only show up if the organism doesn't have the
dominant allele
.
Probability:

the likelihood that a particular event will occur
Punnett square:

a chart that shows all the possible combinations of alleles that can result from a genetic cross
Phenotype:

an organism's physical appearance, or visible traits
Genotype:
an organism's genetic makeup, or allele combinations
Heterozygous:

having two different alleles for a trait
Homozygous:
having two identical alleles for a trait
Codominance:
a condition in which neither of two alleles of a gene is dominant or recessive
Phenotypes & Genotypes
An organism's
genotypes
are the codes for its
phenotypes.
Geneticists use the terms
heterozygous
and
homozygous
to describe and organism's genotype.
*** A way to remember the difference is "geno" as in gene and "pheno" as physical.
The Cell & Inheritance
Key Terms
Meiosis:
the process that occurs in sex cells (sperm and egg) by which the number of chromosomes is reduced by half
Chromosome:
a doubled rod of condensed chromatin; contains DNA that carries genetic information

According to the chromosome theory of inheritance, genes are carried from parents to their offspring on
chromosomes
The body cells of grasshoppers have 24 chromosomes, 12 of which are in the sex cell
The 24 chromosomes of the grasshopper offspring exist in 12 pairs; one chromosome in each pair from the male parent, and the other from the female parent
Meiosis
During
meiosis
, the chromosome pairs separate an are distributed to two different cells
The resulting sex cells have only half as many chromosomes as the other cells in the organism
Chromosomes
Chromosomes are made up of many genes joined together like beads on a string
Humans have 23 pairs of chromosomes, or 46 chromosomes total
Genes are lined up in the same order from one end of the chromosome to the other
One chromosome in the pair comes from the female; the other from the male
The DNA Connection
The main function of genes is to control the production of proteins.
Proteins help to determine the size, shape, and many other traits.
The order of the nitrogen bases along a gene form a genetic code made up of
amino acids
.
The order of the bases also determines the order in which amino acids are put together to form a protein.
Key Terms
Amino acid:
small molecules that are linked together chemically to form proteins; the building blocks of proteins
Messenger RNA:
RNA that copies the coded message from DNA in the nucleus and carries the message into the cytoplasm
Transfer RNA:
RNA in the cytoplasm that carries an amino acid to the ribosome and adds it to the growing protein chain
RNA:
Ribonucleic acid; nucleic acid that plays an important role in the production of proteins
Protein synthesis:
the production of proteins
Protein Synthesis
During
protein synthesis
, the cell uses information from a gene on a chromosome to produce a specific protein.
Step 1: Transcription - the genetic code is copied off a strand of DNA and onto the messenger RNA in the cell's nucleus
Step 2: Translation - the
messenger RNA
leaves the nucleus and travels to ribosomes in the cytoplasm where the coded info is translated into specific amino acid sequences to form protein
Mutations
Phenotype(s) will be different
Result of small changes in heredity material
Result of when chromosomes don't separate correctly during meiosis ex -end up with too little or too many chromosomes
Some changes brought by mutations are harmful to an organism while others are helpful. Some are neither harmful or helpful
In his first experiment Mendel crossed purebred self pollinating tall
plants with purebred self pollinating short plants. He called the offspring from this cross the
F1 generation (first filial)

All of the offspring were tall even though one parent was short.

The short trait disappeared!

F1 Generation
Mendel crossed the plants of the F1 generation and got another surprising result.
He found that 3/4 of the plants were tall while 1/4 of the plants were short.
The second generation is called the F2 generation.

F2 Generation

Gregor Mendel
WHAT IS DNA AND HOW DOES IT WORK?
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