Biology Chapter 14 Flashcards
Who first studied genetics?
Gregor Mendel
When did Gregor Mendel study genetics?
1850 - 1870
What did Gregor Mendel use to study genetics?
Peas
Mendels genetic factors proved in 1952 to be
DNA
DNA is divided into
Genes
Each gene has the code for making what?
One protein
Human DNA has roughly how many genes?
25,000
Genes can be several alternative types called
Alleles
Examples of alleles are
Allele B for brown hair
Allele b for blonde hair
How many alleles do you inherit?
2 (one from each parent)
Dominant allele
Has an effect whether you have one copy or two (BB or Bb, brown hair)
Recessive allele
Only has an effect if you inherit two copies (bb, blonde hair)
Genetics
The study of inheritance
Genotype
The genetic makeup of an individual (Bb)
Phenotype
The physical appearance of an individual (brown hair)
Homozygous dominant
Two capital letters
Heterozygous
One capital, one lower case
Homozygous recessive
Two lower case letters
Mendel’s first law of genetics
Different characteristics are caused by different alleles
Mendel’s second law of genetics
An organism inherits two alleles for each trait
Mendel’s third law of genetics
Each gamete only contains one allele for each trait
Mendel’s fourth law of genetics
In a heterozygous individual, only the dominant allele affects the trait
Monohybrid cross how many traits are studied?
Only one trait is studied
Dihybrid cross how many traits are studied?
Two traits are studied
Test cross
Used to work out an unknown genotype (dominant phenotype)
What is the unknown genotype crossed with?
A homozygous recessive individual
If all the offspring have the dominant phenotype, the unknown parent must be
Homozygous dominant
If some of the offspring have the recessive phenotype, the unknown parent must be
Heterozygous
Dihybrid cross
Each trait is inherited independently
How many possible phenotypes in the dihybrid cross offspring?
Four
In a dihybrid cross, if two heterozygous individuals are crossed the result is a ratio of
9:3:3:1
Punnett squares work out the
Probability of getting a particular offspring
If two heterozygous individuals breed
3/4 of offspring will have the dominant trait and 1/4 will have the recessive trait
If two heterozygous people have children
Each child has a 1 in 4 (1/4) chance of being blonde
For a dihybrid cross
You multiply the probabilities together
Incomplete dominance
Both alleles affect the phenotype
Homozygous dominant (red) looks different from
Heterozygous (pink)
Both incomplete dominance alleles have
Capital letters
If two heterozygous individuals are crossed in a state of incomplete dominance the offspring are in the ratio
1:2:1
Polygenic inheritance
Trait is affected by several genes so the offspring of heterozygous parents can be very different from either parent
A graph of the expected offspring from heterozygous parents follows a normal distribution curve
Examples: skin color, height
Where are genes located?
Chromosomes
Different species have different numbers of — but about the same amount of —.
Chromosomes, DNA
A typical human chromosome has roughly how many genes on it?
1000
Linked genes are on the sam
Chromosome
Linked genes tend to be
Inherited together
How are linked genes separated?
By crossing over in Prophase I
What gives different results from the Punnett square prediction?
Linked genes being separated
How does a genetic map gives the location of genes?
By working out the frequency of crossing over
About what percent of a chromosome is genes?
10%
What percent of the originally unknown (junk DNA) is active?
80%
Most chromosomes consist of switches that turn what on and off?
Genes
How many genetic switches are in human DNA?
4 million
Non-sex chromosomes are called
Autosomal
How many pairs of non-sex chromosomes do both men and women human cells have?
22 pairs
How many pairs of sex chromosomes do human cells have?
1 pair
The sex chromosomes in the female are
XX
The sex chromosomes in the male are
XY
X chromosomes have how many genes?
Over 1000 genes
How many genes are in Y chromosomes?
Less than 80 genes
What percent of human births are male?
52%
What percent of human births are female?
48%
Why is there a higher percent of male births than female births?
Sperm carrying the Y chromosome are lighter and swim faster than ones with the X chromosome
Sex linked diseases mainly affect
Men
Sex linked diseases are caused by recessive genes on the
X chromosome
Women have — copies of X while men have — copies of X.
2,
1
Sex-linked diseases are usually passed on from a carrier female to her
Son
What percent of men are colorblind?
8%
What percent of women are colorblind?
0.5%
Hemophilia
Blood does not clot
How many X chromosomes are active in women?
1
What does the other X chromosome in women do?
Condensed to form the Barr body
Where is the Barr body?
The edge of the nucleus
Are the genes in the Barr body active or inactive?
Inactive
Heterozygous females can have different — active in different parts of the body
X chromosomes
What are Barr bodies used for?
To test for gender in sporting events like the Olympics, to make sure competitors a really are female
Some genes have different effects depending on whether they are inherited from the mother or father. What are these genes called?
Genomic imprinting (the genes are imprinted)
During genomic imprinting,
Some of the fathers genes are switched off and some of the mothers genes are switched off
What will happen If two sperm or two eggs join
The embryo will not survive
Mice with mainly the fathers genes have
Small heads and large bodies
Mice with mainly the mothers genes have
Small bodies and large heads
Mice with male imprinted genes affect
Lower parts of the brain (feeding, reproduction, emotions)
Mice with female imprinted genes affect
The higher brain (thinking, memory)
Human male imprinted genes
Increase the size of babies
Human female imprinted genes
Reduce the size of babies
