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INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12. Quick review…. Genetics is the field of biology devoted to understanding how characteristics are transmitted form parents to offspring. Generations: P Tall x Short F1 Tall (tall is dominant) F2 3 Tall : 1 short.
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Quick review… Genetics is the field of biology devoted to understanding how characteristics are transmitted form parents to offspring.
Generations: P Tall x Short F1 Tall (tall is dominant) F2 3 Tall : 1 short • The DOMINANT factor/gene masks the effect of the other factor in the F1 generation. • Use CAPS ex. T for tall • The RECESSIVE factor/gene’s effect can only be seen in the P generation or F2 generation when the DOMINANT gene is absent. • Use lower case ex. t for short
MENDEL’S 2 LAWS: #1 LAW OF SEGREGATION: #2 LAW OF INDEPENDENT ASSORTMENT: • A pair of factors is segregated, or separated, during the formation of gametes. • Factors for different characteristics are distributed to gametes independently.
GENOTYPE is the genetic makeup of the organism. TT = homozygous dominant Tt = heterozygous tt = homozygous recessive PHENOTYPE is the physical appearance of that organism. Ex. Tall or short MENDELIAN INHERITANCE- DOMINANCE…. 2 phenotypes only. If someone has the dominant phenotype but you aren’t sure of Their genotype… use a pedigree (humans) or do a test cross.
Other Patterns of Inheritance: • Incomplete Dominance- blending seen in heterozygote (ex. pink flowers, brown hair) • Codominance- both dominant and recessive phenotypes seen in heterozygote. (ex. type AB blood, roan horse fur color) • Polygenic- more than 1 gene determines the phenotype. (Ex. Eye color, Hair color aabbcc) • Multiple alleles- more than just 2 alleles (Ex. Blood type = A allele, B allele, O allele is recessive.)
EX. Polygenic Inheritance- when the trait is controlled by multiple genes so many phenotypes are possible. AaBbCc x AaBbCc Huge variety in possible Phenotypes of the offspring - skin, hair, eye color - foot size - nose length - height
Multiple alleles- trait controlled by three or more alleles. -Ex. ABO blood groups: - TYPE A - TYPE B - TYPE AB Shows Codominance! - TYPE O
When someone has the DOMINANT phenotype you are uncertain of their genotype. TT or Tt When someone has the recessive phenotype you can be sure of their genotype. tt The process of using phenotypes to deduce genotypes
DIRECTIONS: • For each of the following single gene/ Mendelian traits, write your phenotype on the line. • Write as much of your genotype as you can be certain. - both alleles if RECESSIVE (rr) - one allele if DOMINANT (R __) • Repeat the process by studying two blood relatives (parents work the best) • Use a pedigree.
13. Hypermobility of ThumbLoose Jointed or Not soHH, Hh hh
LIST OF STRANGE MENDELIAN TRAITS • Ear wiggling • Misshapen toes or teeth • Inability to smell musk or skunk • Lack or teeth, eyebrows, nasal bones or thumbnails • Whorl in the eyebrow • Tone Deafness • Hairs that are triangular in cross-section or that have multiple hues (colors) • Hairy knuckles, palms, soles, or elbows • Egg-shaped pupils • Magenta urine after eating beets • Sneezing fits in bright sunlight.
DNA in chromosomes contain information to make proteins. Geneticists use their knowledge of DNA and the way chromosomes behave to study how traits are inherited and expressed.
The parent’s genotype can be a gene pair of either: - TT homozygous dominant - tt homozygous recessive - Tt heterozygous The parent can make gametes (sperm or eggs), through the process of MEIOSIS, that have either one or the other of the gene pair in it.
SEX DETERMINATION MORGAN’s Fruit fly (Drosophila) breeding experiments of the 1900’s revealed the identity of sex chromosomes. In males they were different XY; in females they were the same XX. The other chromosomes (22 in humans) are AUTOSOMES.
The male determines the sex of the offspring… <--The FEMALE XX can only make X gametes. <--The MALE XY can make either X gametes or Y gametes.
SEX LINKAGE traits caused by genes found on a sex chromosome X-LINKED GENES: Genes located on the X chromosome. • Women can be carriers. • Ex. gene for ALD (Lorenzo’s Oil) Y-LINKED GENES: Genes located on the Y chromosome. Only males show these traits. Ex. SRY- triggers male development of testis.
Males exhibit X-linked traits more often than women because they only have ONE X chromosome. • Females have two XBXb or sex linked genes. • Females can be “carriers” of the bad gene yet not show the disease.. • Males only have one X or sex linked gene since they are XbY. • Males have a higher chance of having the condition than if it were on an autosome. • THERE IS NO HETEROZYGOUS for men.
X-linked Examples: • Eye color in Drosophila • Red-green colorblindness • Male Pattern Baldness • Hemophilia • Duchenne Muscular Dystrophy • ALD (adreno leuko dystrophy)
If a carrier (woman) for hemophilia marries a normal man, what are the chances of having kids who are hemophiliacs? Who are not?What if the man is a hemophiliac???????
LINKAGE GROUPS Genes located on the same chromosome are said to be linked. Linked genes tend to be inherited together. Examples: Hair color and intelligence are linked in humans. fur color and deafness in cats are linked.
I’m kidding about intelligence and hair color being linked. • But if they were linked… • What would the phenotype(s) be of children of a dumb,blonde & smart,brunette
smart,brunette • If that smart,brunette had kids w/ a dumb,blonde What kinds of kids could they have? What is the probability of each?
Parental Phenotypes: • Smart, brunette • Dumb, blonde Recombinant Phenotypes: • Smart, blonde • Dumb, brunette
Linked genes result in traits that tend to be inherited together… If you do a test cross of your Heterozygote you can see if the genes Are linked (5:5:1:1) or not (1:1:1:1). If the intelligence and hair color genes were linked, we’d only see smart-brunettes and dumb-blondes. (HA HA) So, since there are smart blondes- are these genes on separate chromosomes or on the same chromosome yet separated by crossing over?????
Chromosome maps can be created by conducting breeding experiments. Linked genes that separate by crossing over X% of the time are X map units apart. Compare 4 phenotype inheritance to 2 phenotype inheritance. Genes can now be placed on a chromosome in some order.
Genes W and Z separate by crossing over 20% of the time. • Genes W and X separate by crossing over 5% of the time, and • genes Z and X are separated by crossing over 25% of the time. • CONSTRUCT A CHROMOSOME MAP. • Z W X • I----20-------I--5--I
Mutations, Disease, & Human Mendelian Traits • Where they occur/ significance. • Types: Chromosome or Gene • Diseases & Inheritance Patterns. • Using Phenotypes to deduce Genotypes
Germ cell mutation • occurs in the gametes • does not effect the organism • may be passed on to offspring if fertilized • Somatic mutation • occurs in the organism’s body cells & can affect the organism • ex. Skin cancer & leukemia • are not passed on to offspring • Lethal mutation • causes death (often before birth) • is not passed on if death occurs before reproduction • Beneficial mutation • result in phenotypes that are beneficial. • beneficial phenotypes lead to increased reproduction.